Fix doc gen, making multilib test happy during packaging.

Closes #771.

Multilib regressions were reported by rpmdiff.
One of them was that xmlto generated random anchor names, like this one:

...<div class="refsect2"><a name="idm139684544026160"></a><h3>Methods</h3>...

This caused e.g. abrt-dbus package to contian different files
for x86_64 vs i686, making it impossible to install both on one machine.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Do not copy Makefiles to documentation.

Closes #771.

Multilib regressions were reported by rpmdiff.
Makefiles were leaking into /usr/share/doc/abrt-devel-N.N.N.
This caused e.g. abrt-dbus package to contian different files
for x86_64 vs i686, making it impossible to install both on one machine.

...<div class="refsect2"><a name="idm139684544026160"></a><h3>Methods</h3>...

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>