Fix minor compilation problems in extras and benchmarks.

These are due to:

- differences between module and file names.
- redundant imports
- the recent change from math.domain_error -> exception.domain_error.

benchmarks/*/*.m:
extras/*/*.m:
    As above.

benchmarks/progs/fibonacci/fib_par_plain.m

@@ -1,5 +1,5 @@
 
-:- module fib_plain_par.
+:- module fib_par_plain.
 
 :- interface.
 

benchmarks/progs/icfp2000/eval_util.m

@@ -19,7 +19,7 @@
 
 :- implementation.
 
-:- import_module int, list, exception, map, string, gml.
+:- import_module int, list, exception, map, string.
 :- import_module pprint.
 
 write_nice_exception(E) -->

benchmarks/progs/icfp2000/renderer.m

@@ -31,7 +31,7 @@
 :- import_module transform_object, gml, op.
 :- import_module precompute_lights.
 :- import_module map, array, exception, require, math.
-:- import_module int, float, list, std_util, string.
+:- import_module int, float, std_util, string.
 
 render(Params1) -->
 	{ Wid = Params1 ^ wid },

benchmarks/progs/icfp2000/trans.m

@@ -198,7 +198,7 @@
 
 :- implementation.
 
-:- import_module exception, string, math, list, std_util.
+:- import_module exception, string, math, std_util.
 
     % NOTE 1: points and vectors are represented using the point/3 type
     % defined in eval.m.  For the purposes, a point (x, y, z) is

benchmarks/progs/icfp2001/input.m

@@ -76,7 +76,7 @@
 
 :- implementation.
 
-:- import_module int, list, char, exception, string, bool.
+:- import_module int, exception, string, bool.
 :- import_module maybe.
 :- import_module pair.
 

benchmarks/progs/ray/gfx.m

@@ -86,7 +86,7 @@
 
 :- implementation.
 
-:- import_module require, string.
+:- import_module require.
 
 colour(R1, G1, B1) + colour(R2, G2, B2) = colour(R1 + R2, G1 + G2, B1 + B2).
 

extras/base64/base64.m

@@ -45,7 +45,6 @@
 :- import_module exception.
 :- import_module float.
 :- import_module int.
-:- import_module list.
 :- import_module map.
 :- import_module require.
 :- import_module std_util.

extras/gmp_int/gmp_int.m

@@ -200,7 +200,7 @@
 :- func invmod(gmp_int, gmp_int) = gmp_int.
 
     % Exponentiation.
-    % Throws exception `math.domain_error` if Y is negative.
+    % Throws exception `exception.domain_error` if Y is negative.
     %
 :- func pow(gmp_int, gmp_int) = gmp_int.
 
@@ -296,7 +296,6 @@
 
 :- import_module exception.
 :- import_module int.
-:- import_module math.
 :- import_module require.
 
 %---------------------------------------------------------------------------%
@@ -523,7 +522,7 @@
     ( to_int(A, Res0) ->
         Res0 = Res
     ;
-        throw(math.domain_error("gmp_int.det_to_int: not in int range"))
+        throw(domain_error("gmp_int.det_to_int: not in int range"))
     ).
 
 :- pred fits_in_long(gmp_int::in) is semidet.
@@ -556,7 +555,7 @@
     ( ( R >= 2, R =< 62 ) ->
         S = gmp_to_base_string(A, R)
     ;
-        throw(math.domain_error("gmp_int.to_base_string: base must be between 2 and 62"))
+        throw(domain_error("gmp_int.to_base_string: base must be between 2 and 62"))
     ).
 
 :- func gmp_to_base_string(gmp_int, int) = string.
@@ -785,7 +784,7 @@
     ( sqrt(A, Root) ->
         Res = Root
     ;
-        throw(math.domain_error("gmp_int.det_sqrt: number must be non-negative"))
+        throw(domain_error("gmp_int.det_sqrt: number must be non-negative"))
     ).
 
 :- pred gmp_sqrt(gmp_int::in, gmp_int::out) is det.
@@ -809,7 +808,7 @@
     ( nthroot(A, N, Root) ->
         Res = Root
     ;
-        throw(math.domain_error("gmp_int.det_sqrt: number must be non-negative"))
+        throw(domain_error("gmp_int.det_sqrt: number must be non-negative"))
     ).
 
 :- pred gmp_nthroot(gmp_int::in, int::in, gmp_int::out) is det.
@@ -835,7 +834,7 @@
 
 pow(A, N) = Res :-
     ( is_negative(N) ->
-        throw(math.domain_error("gmp_int.pow: cannot handle negative exponent"))
+        throw(domain_error("gmp_int.pow: cannot handle negative exponent"))
     ;
         Res = pow2(A, N)
     ).

extras/graphics/easyx/easyx.m

@@ -386,7 +386,6 @@
 :- import_module exception.
 :- import_module float.
 :- import_module int.
-:- import_module list.
 :- import_module math.
 :- import_module store.
 :- import_module string.

extras/lex/lex.m

@@ -27,7 +27,6 @@
 :- import_module char.
 :- import_module io.
 :- import_module list.
-:- import_module maybe.
 :- import_module pair.
 :- import_module string.
 :- import_module sparse_bitset.
@@ -270,11 +269,11 @@ func re(T) = regexp
 
 :- import_module array.
 :- import_module bool.
-:- import_module char.
 :- import_module exception.
 :- import_module require.
 :- import_module int.
 :- import_module map.
+:- import_module maybe.
 
 :- import_module lex.automata.
 :- import_module lex.buf.

extras/net/types.m

@@ -191,7 +191,6 @@ pred to_string(A::in, string::uo) is det
 :- implementation.
 
 :- import_module bool.
-:- import_module int.
 :- import_module require.
 
 :- import_module net.errno.