* Makefile.in: Add a 'check' target that builds and runs

	* Makefile.in: Add a 'check' target that builds and runs
	testsuite.exe from path-testsuite.o and testsuite.o.
	* path.cc: Include testsuite.h.
	(struct mnt): Change to a mnt_t typedef and don't define
	mount_table when TESTSUITE is defined.
	(find2): Don't include when TESTSUITE is defined to avoid warning.
	(get_cygdrive0): Ditto.
	(get_cygdrive): Ditto.
	(read_mounts): Provide empty implementation when TESTSUITE is
	defined.
	(vconcat): Use the isslash macro.
	(unconvert_slashes): New helper to convert to backslashses.
	(rel_vconcat): Handle relative paths more gracefully.
	(cygpath): Skip a leading "./" sequence.  Avoid double-slashes.
	Normalize final output to backslashes and remove redundant path
	sequences.
	* testsuite.cc: New file implementing testsuite driver.
	* testsuite.h: New header implementing harness mount table and
	series of tests.