Allow to clone repositories that don't have a `master` branch

Before this, we error out from `reference_matches_remote_head` if the
reference we're searching for does not exist.
Since we explicitly check if master is existing in `update_head_to_remote`
and error out if it doesn't, a repository without master branch could
not be cloned.
In fact this was later clobbered by what is fixed in #1194.

However, this patch introduces a `found` member in `head_info` and sets
it accordingly. That also saves us from checking the string length of
`branchname` a few times.
travis: Include the online suite when running against Travis
clone: Fix a memory leak
tests: Fix some memory leaks
reset: Fix a memory leak
Merge pull request #1197 from nulltoken/travis/run-online-tests

travis: Include the online suite when running against Travis
Merge pull request #1196 from scunz/allow_clone_without_master_branch

Allow to clone repositories that don't have a `master` branch
travis: Only run Valgrind when all tests pass
Merge pull request #1198 from nulltoken/travis/run-valgrind-on-success

travis: Only run Valgrind when all tests pass
Tab align value of GIT_FILEMODE_BLOB_EXECUTABLE
Revert "Tab align value of GIT_FILEMODE_BLOB_EXECUTABLE"

This reverts commit 47fbcbb5a8d4aad87371a381ebdadd04cde3fb2b.
Correct typos in documentation
merge cleanup should actually cleanup and the test should actually test
Merge pull request #1200 from ethomson/merge_cleanup

merge cleanup should actually cleanup and the test should actually test
Add Florian Forster to hall of fame

Permission recieved from Florian Forster on Jan 07 2013 to include
any changes of his from core Git into LibGit2.
Revert changes from git/git diff-delta.c by dak@gnu.org, proski@gnu.org
Merge pull request #1202 from martinwoodward/add-florian

Add Florian Forster to hall of fame
Merge pull request #1203 from phkelley/reverse_dak

Revert changes from git/git diff-delta.c by dak@gnu.org, proski@gnu.org
Introduce git_diff_blob_to_buffer
Share git_diff_blobs/git_diff_blob_to_buffer code

This moves the implementation of these two APIs into common code
that will be shared between the two.  Also, this adds tests for
the `git_diff_blob_to_buffer` API.  Lastly, this adds some extra
`const` to a few places that can use it.