Escape slashes in filters

Simply escape slashes in --filter-requires and --filter-provides
options, resolving a five year old bug [0].

[0] https://bugzilla.redhat.com/show_bug.cgi?id=544738

Signed-off-by: Petr Šabata <contyk@redhat.com>
Merge pull request #6 from contyk/master

Escape slashes in filters