RPM version numbers

We now have functions for converting between Buzzy version numbers and
RPM version numbers.  The RPM version comparison algorithm is defined in
[1], and RedHat provides additional guidance in selecting version
numbers at [2].  RPM version strings are most restrictive than Buzzy
version strings: Buzzy lets you have as many pre- and post-release tags
as you want, in any order within the version.  RPM does not really have
a separate concept of pre- and post-release tags, so we have to mimic
those by the version parts that we do have available.

This means that the new functions are not reversible — if you convert a
Buzzy version into an RPM version, and then back, you don't get the same
result.  However, if you convert once in either direction, we can
guarantee that a version comparison will be the same before and after
the conversion.

[1] http://fedoraproject.org/wiki/Archive:Tools/RPM/VersionComparison
[2] https://fedoraproject.org/wiki/Packaging:NamingGuidelines#Package_Versioning
Native RPM packages

We now have a package database that can use RPM and yum to install
native packages on RPM-based systems.  I'm currently only testing things
on RHEL, but we should add some other RPM systems to be more thorough.
Don't use `cmake --target`

Our cmake builder now assumes that we'll end up with Makefiles in the
build directory, and runs `make` directly to build, test, and stage the
package.  Before, we were using cmake's `--target` option to let cmake
decide which command to run to perform the actual build.  But this
option wasn't added until cmake 2.8, which isn't (easily) available on
some of the platforms we want to support.
RPM packager

We now have an implementation of the packager interface that can create
RPMs for our built packages on the various RedHat flavors of Linux.  We
don't let RPM perform the actual build, since that's already handled by
our builder implementations.  We just have `rpmbuild` package up the
resulting staging directory into a new binary package.
Merge branch 'feature/c-rhel' into develop

* feature/c-rhel:
  RPM packager
  Don't use `cmake --target`
  Native RPM packages
  RPM version numbers
Forward SSH agent to Vagrant VMs