Have PackageModule.__init__() extract the args.path
itself.

'fedpkg local-init' initalizes a local git repo to use with (most)
fedpkg commands.

The definition of the --path argument to fedpkg in parse_cmdline()
already makes os.getcwd() the default value for args.path.

Thus, we can get rid of the code providing the very same default
for the path in PackageModule.__init__().

Also, make sure the path actually exists and is a directory.

This avoids unnecessary lookup of non-existing users and
the resulting error messages in mock builds.

Add an option '--fix-permissions' to the 'fedpkg srpm' call.

If the '--fix-permissions' option is not given, the behaviour
of 'fedpkg srpm' does not change at all.

If the '--fix-permissions' option is given, fedpkg runs

   git ls-files -z | xargs -0 chmod a+r

before running the normal rpmbuild command. This makes sure
that all 0600 files the filesystem are changed to the usual
0644 before including them in .src.rpm file.

Unify handling of the --md5 parameter between the two targets using it:
'fedpkg local' and 'fedpkg srpm'.

If no --md5 parameter is given, then the default hashtype is used, as
determined in PackageModule.__init__() ('md5' for el5 and el6, and
'sha256' for everything else).

If an --md5 parameter is given, then use the 'md5' hashtype.

Add man page generator to generate a man page at build time.