[RFE]: provide API to SPEC file parser

Description of problem:

For "third party tools" (like TPS) there's sometimes need to access to the
resulting string from Release line in SPEC file.

Input is SPEC file with this lines

%define _extra_release %{?dist:%{dist}}%{!?dist:%{?extra_release:%{extra_release}}}
Release: 3%{_extra_release}.1

Output is .el5_1.1 or The Right String.

See this bug 441672.

Version-Release number of selected component (if applicable):
rpm-4.4.2-48.el5

How reproducible:
always

Actual results:
no exported API

Expected results:
exported API

Sure there's an API of sorts for this in librpmbuild (even if it's not exactly
very sane or friendly to use), but just for digging out a release number from a
spec you can use a spec query, for example:

[pmatilai@localhost RHEL-5]$ rpm -q --define "%dist .el5" --specfile --qf
"%{name} %{version} %{release}\n" virt-manager.spec
virt-manager 0.5.3 7.el5
virt-manager-debuginfo 0.5.3 7.el5

NOTABUG in the sense that couple of ways to access this data do exist. There are
plans to provide a saner API for the build parts for rpm (including python
bindings), but that's way way out of scope for RHEL 5.