Add pixman dependency.
Otherwise, it tries to use the included copy, but fails because autoreconf
is not found.
Changes 1.8.1.1:
* The attribute mechanism didn't allow limiting attributes to be
  applied to only a single directory itself with "path/" like the
  exclude mechanism does.
* When attempting to read the XDG-style $HOME/.config/git/config and
  finding that $HOME/.config/git is a file, we gave a wrong error
  message, instead of treating the case as "a custom config file does
  not exist there" and moving on.
* After failing to create a temporary file using mkstemp(), failing
  pathname was not reported correctly on some platforms.
* http transport was wrong to ask for the username when the
  authentication is done by certificate identity.
* The behaviour visible to the end users was confusing, when they
  attempt to kill a process spawned in the editor that was in turn
  launched by Git with SIGINT (or SIGQUIT), as Git would catch that
  signal and die.  We ignore these signals now.
* A child process that was killed by a signal (e.g. SIGINT) was
  reported in an inconsistent way depending on how the process was
  spawned by us, with or without a shell in between.
* After "git add -N" and then writing a tree object out of the
  index, the cache-tree data structure got corrupted.
* "git apply" misbehaved when fixing whitespace breakages by removing
  excess trailing blank lines in some corner cases.
* A tar archive created by "git archive" recorded a directory in a
  way that made NetBSD's implementation of "tar" sometimes unhappy.
* When "git clone --separate-git-dir=$over_there" is interrupted, it
  failed to remove the real location of the $GIT_DIR it created.
  This was most visible when interrupting a submodule update.
* "git fetch --mirror" and fetch that uses other forms of refspec
  with wildcard used to attempt to update a symbolic ref that match
  the wildcard on the receiving end, which made little sense (the
  real ref that is pointed at by the symbolic ref would be updated
  anyway).  Symbolic refs no longer are affected by such a fetch.
* The "log --graph" codepath fell into infinite loop in some
  corner cases.
* "git merge" started calling prepare-commit-msg hook like "git
  commit" does some time ago, but forgot to pay attention to the exit
  status of the hook.
* "git pack-refs" that ran in parallel to another process that
  created new refs had a race that can lose new ones.
* When a line to be wrapped has a solid run of non space characters
  whose length exactly is the wrap width, "git shortlog -w" failed
  to add a newline after such a line.
* The way "git svn" asked for password using SSH_ASKPASS and
  GIT_ASKPASS was not in line with the rest of the system.
* "gitweb", when sorting by age to show repositories with new
  activities first, used to sort repositories with absolutely
  nothing in it early, which was not very useful.
* "gitweb", when sorting by age to show repositories with new
  activities first, used to sort repositories with absolutely
  nothing in it early, which was not very useful.
* When autoconf is used, any build on a different commit always ran
  "config.status --recheck" even when unnecessary.
* Some scripted programs written in Python did not get updated when
  PYTHON_PATH changed.
* We have been carrying a translated and long-unmaintained copy of an
  old version of the tutorial; removed.
* Portability issues in many self-test scripts have been addressed.
Updated devel/scmgit to 1.8.1.1