Add the repository-specific git config include (git >= 1.7.10)

!!! NOTE - potential security RISK !!!

 You *MUST*
  - check the file is legit:
     git diff 7eb1f0e165a4 maint/git_config_dbic.inc

  - copy the file to your .git directory:
     cp maint/git_config_dbic.inc .git/

  - and include it:
     git config --add include.path git_config_dbic.inc

 **NEVER** include the file directly from the repository itself, e.g.

 [include]
   path = ../maint/git_config_dbic.inc

!!! NOTE - potential security RISK !!!

Adds extra maint-specific repositories, and defines two gitk shortcuts:

 `git vis` - showing all current heads/stashes of interest in progress
 `git prvis` - showing all unattended to github PRs

maint/git_config_dbic.inc

@@ -0,0 +1,44 @@
+[remote "ghpr"]
+  url = https://github.com/dbsrgits/DBIx-Class
+  pushurl = DISALLOWED
+  fetch = +refs/pull/*/head:refs/remotes/ghpr/*
+
+[remote "historic"]
+  url = git://git.shadowcat.co.uk/dbsrgits/DBIx-Class-Historic.git
+  pushurl = ssh://dbsrgits@git.shadowcat.co.uk/DBIx-Class-Historic.git
+  fetch = +refs/heads/*:refs/remotes/historic/*
+
+[remote "debian"]
+  url = git://anonscm.debian.org/pkg-perl/packages/libdbix-class-perl.git
+  pushurl = DISALLOWED
+  fetch = +refs/heads/master:refs/remotes/debian/master
+  tagopt = --no-tags
+
+[alias]
+  # Lines after gitk in order:
+  #
+  # --exclude all refs matching the for loop
+  # all known refs (branches/tags) excepth what we excluded
+  # add all individual stashes
+  # add all github PR heads without a matching historic/ghpr/* entry
+  #
+  # the /bin/true at the end is there to eat away any args to 'vis'
+  # ( otherwise they will be treated as commands to execute after the & )
+  vis = "!gitk \
+    $( for r in historic/ghpr ghpr debian ; do echo "--exclude=refs/remotes/$r/*" ; done ) \
+    --all \
+    $(git stash list | cut -f 1 -d ':') \
+    $(/bin/bash -c \"/usr/bin/comm -23 \
+      <(git for-each-ref --sort=objectname --format='%(objectname:short)' refs/remotes/ghpr/ ) \
+      <(git for-each-ref --sort=objectname --format='%(objectname:short)' refs/remotes/historic/ghpr/ refs/remotes/origin/ ) \
+    \") \
+  \"$@\" & /bin/true"
+
+
+  # same but only for GitHub PRs
+  prvis = "!gitk \
+    $(/bin/bash -c \"/usr/bin/comm -23 \
+      <(git for-each-ref --sort=objectname --format='%(objectname:short)' refs/remotes/ghpr/ ) \
+      <(git for-each-ref --sort=objectname --format='%(objectname:short)' refs/remotes/historic/ghpr/ refs/remotes/origin/ ) \
+    \") \
+  \"$@\" & /bin/true"