Don't assume that if guestfs_case_sensitive_path returns NULL, that it
means the file does not exist.

The (previously undefined) behaviour of case_sensitive_path was that a
NULL return meant "either the file doesn't exist or some other error".
However in commit 973581780d8a006f336684fef6762801402d775d this was
changed so that if the last element of the path didn't exist, it was
assumed to be a new file and the (non-NULL) path of the new file is
returned.

This change breaks code (including in libguestfs) which tries to use
case_sensitive_path as a dual-purpose call to fix-up a path for
Windows and test if the file exists.  Such code should be rewritten so
that it explicitly tests for file existence after calling
case_sensitive_path.

I examined all the calls to case_sensitive_path in libguestfs and
modified them where necessary.

For some reason these tests did not have license notices.

This also makes the test for license "code" less strict, so it should
only match POD, not Perl comments.

This fixes commit 2f97bf873b64384835f257f8916bf1ebb2af62b4.

This adds standard LICENSE and BUGS sections to all of the man pages
that are processed by podwrapper.

Modify all the calls to $(PODWRAPPER) to add the right --license
parameter according to the content.  Note that this relaxes the
license on some code example pages, making them effectively BSD-style
licensed.

The compress flag can be used to control compression, one of: (none),
"compress", "gzip", "bzip2", "xz", "lzop".  Thus these calls can now
be used instead of tgz-in/tgz-out/txz-in/txz-out, and also support
more compression types.

Mark these APIs as once_had_no_optargs so that compatibility code is
generated.

This problem has been fixed in
commit 50780a84f65ec5d76605691cea889392c2730f54.

This will allow us to easily change the location of this
script in future.