buildpackage-rpm: add more tagging options

buildpackage-rpm: add more tagging options

Add new possible keywords to be used in packaging-tag format string:
'nowtime', 'authortime', 'committime', 'nowtimenum', 'authortimenum' and
'committimenum'.

The '*timenum' keyword denote the corresponding '*time' keyword appended
with an additional incremental serial number. E.g. if 'nowtime' would
produce '20120531', 'nowtimenum' would (the first time) produce
'20120531.1'.

What is completely missing is a way to support these new tag keywords in
git-import-srpm tool. So, if you use these tags, git-import-srpm is not
able to reproduce the tags, (and, it is not necessarily able to
correctly tell if you've already imported a certain version of the
package).

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>