rpms: add hgext3rd to mercurial.spec
Otherwise build process fails with somethings like this:
RPM build errors:
Installed (but unpackaged) file(s) found:
/usr/lib64/python2.7/site-packages/hgext3rd/__init__.py
/usr/lib64/python2.7/site-packages/hgext3rd/__init__.pyc
/usr/lib64/python2.7/site-packages/hgext3rd/__init__.pyo
make: *** [docker-fedora20] Error 1
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.