Enhance the buildconf force option

The force option used to only remove the Autoconf cache files. Now it
also removes entire configure file so the configure file always gets
rebuilt when needs be done.

Additionally, the buildconf now also accepts the shorter version of the
force option:
  buildconf -f

buildconf

@@ -38,7 +38,7 @@ SYNOPSIS:
   buildconf [<options>]
 
 OPTIONS:
-  --force         Clean cache and overwrite configure files.
+  -f, --force     Clean cache and overwrite configure files.
   --debug         Display warnings emitted by Autoconf.
   -h, --help      Display this help.
 
@@ -55,7 +55,7 @@ HELP
     exit 0
   fi
 
-  if test "$1" = "--force"; then
+  if test "$1" = "-f" || test "$1" = "--force"; then
     force=1
   fi
 
@@ -87,8 +87,8 @@ fi
 
 if test "$force" = "1"; then
   echo "buildconf: Forcing buildconf"
-  echo "buildconf: Removing configure caches"
-  rm -rf autom4te.cache config.cache
+  echo "buildconf: Removing configure caches and files"
+  rm -rf autom4te.cache config.cache configure
 fi
 
 echo "buildconf: Building configure files"