mdoc 2.0-only profile build support, take 3!

Further discussion suggested that, even if mdoc 2.0 works, it hasn't gotten
widespread testing (as it's been a 4.0 app for months), so it would be
preferable to keep it as a 4.0 app.

However, it still needs to be built under 2.0 so that a --with-profile4=no
build can...build...without errors.

Thus, the compromise: build mdoc twice, once for each profile.  This will
ensure that *some* version of mdoc is around when mcs/docs is built.

Unfortunately we can't place mdoc into $(per_profile_dirs), as these are
built before $(net_2_0_dirs) (and thus before monodoc, which needs to be
built before mdoc).  Thus the compromise of listing mdoc in *both*
$(net_2_0_dirs) and $(net_4_0_dirs), allowing build dependencies to be met.

mcs/tools/Makefile

@@ -37,6 +37,7 @@ net_4_0_dirs := \
 	macpack		\
 	dtd2rng		\
 	dtd2xsd		\
+	mdoc		\
 	mod		\
 	installvst	\
 	lc		\

mono-core.spec.in

@@ -1163,7 +1163,7 @@ Monodoc-core contains documentation tools for C#.
 %_mandir/man1/monodocer.1%ext_man
 %_mandir/man1/monodocs2html.1%ext_man
 %_mandir/man5/mdoc.5%ext_man
-%_prefix/lib/mono/2.0/mdoc.exe*
+%_prefix/lib/mono/4.0/mdoc.exe*
 %_prefix/lib/mono/4.0/mod.exe*
 %_prefix/lib/mono/gac/monodoc
 %_prefix/lib/mono/monodoc

scripts/Makefile.am

@@ -56,7 +56,6 @@ scripts_2_0 = \
 	csharp2$(SCRIPT_SUFFIX)			\
 	gacutil2$(SCRIPT_SUFFIX)		\
 	gmcs$(SCRIPT_SUFFIX)			\
-	mdoc$(SCRIPT_SUFFIX)                    \
 	monop2$(SCRIPT_SUFFIX) 			\
 	resgen2$(SCRIPT_SUFFIX)			\
 	wsdl2$(SCRIPT_SUFFIX)
@@ -69,6 +68,7 @@ scripts_4_0 = \
 	installvst$(SCRIPT_SUFFIX)		\
 	genxs$(SCRIPT_SUFFIX)			\
 	macpack$(SCRIPT_SUFFIX)			\
+	mdoc$(SCRIPT_SUFFIX)                    \
 	mono-cil-strip$(SCRIPT_SUFFIX)		\
 	prj2make$(SCRIPT_SUFFIX)		\
 	soapsuds$(SCRIPT_SUFFIX)		\