projtool.pl: add verify command

projtool.pl: add verify command

Provide a verify command in much the same vein as Git's
`git rev-parse --verify` invocation.

When given a project name or path, resolve that to the actual
project, verify that it exists and can be loaded and then show its
canonical project name on standard out and exit with success.

Otherwise exit with an error code.  Diagnostic messages are shown
on standard error unless `--quiet` has been used.

The verify command provides a convenient way to take advantage of
the path-to-project translation facility from the command line.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>