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.
