Makefile: Allow lightweight tags in MXQ_VERSION_GIT

If we build from a git repository, the build system adds the output of
`git describe` to the version information.

However, per default `git describe` searches for annotated tags
only. Since version 0.22.5, we draft releases from github enterprise,
which creates lightweight tags. For this reason, the version string
ammendment was always based on the 0.22.4 release:

    buczek@theinternet:~/git/mxq (master)$ ./mxqd --version
    mxqd - MXQ v0.25.4 (beta) [0.22.4-134-g3ae9361]
      by Marius Tolzmann <marius.tolzmann@molgen.mpg.de> 2013-2016
         and Donald Buczek <buczek@molgen.mpg.de> 2015-2016
      Max Planck Institute for Molecular Genetics - Berlin Dahlem

Add `--tags` to `git describe` so that the version string is based on
the newest tag.

    mxqd - MXQ v0.25.4 (beta) [0.25.4-4-g3ae9361]
      by Marius Tolzmann <marius.tolzmann@molgen.mpg.de> 2013-2016
         and Donald Buczek <buczek@molgen.mpg.de> 2015-2016
      Max Planck Institute for Molecular Genetics - Berlin Dahlem

Makefile

@@ -4,7 +4,7 @@ MXQ_VERSION_PATCH = 4
 MXQ_VERSION_EXTRA = "beta"
 MXQ_VERSIONDATE = 2016
 
-MXQ_VERSION_GIT := $(shell git describe --long 2>/dev/null)
+MXQ_VERSION_GIT := $(shell git describe --long --tags 2>/dev/null)
 
 MXQ_VERSION = ${MXQ_VERSION_MAJOR}.${MXQ_VERSION_MINOR}.${MXQ_VERSION_PATCH}
 ifeq (${MXQ_VERSION_GIT},)