* automake.in: Register "Unified Parallel C" as language.

* automake.in: Register "Unified Parallel C" as language.
(lang_upc_rewrite): New function.
(resolve_linker): Consider UPCLINK.
* lib/Automake/Variable.pm (%_ac_macro_for_var): Suggest
AM_PROG_UPC for UPC and UPCFLAGS.
* m4/upc.m4: New file.
* m4/depend.m4 (_AM_DEPENDENCIES): Add UPC case.
* m4/Makefile.am (dist_m4data_DATA): Add upc.m4.
* doc/automake.texi (Unified Parallel C Support): New node.
(Public macros): Mention AM_PROG_UPC.
(Program and Library Variables, Flag Variables Ordering):
Mention UPCFLAGS.
* tests/upc.test, tests/upc2.test, tests/upc3.test: New file.
* tests/Makefile.am (TESTS): Add them.
* tests/ext.test: Also test upc files.