Composer: allows nette/tester ^1.1

GitRepository: fixed getLastCommitId() on Windows

Method getLastCommitId() returned NULL on Windows.

GitRepository: fixed isRemoteUrlReadable() on non-Windows platforms

GitRepository: added getRemoteBranches()

GitRepository: fixed isRemoteUrlReadable() on Windows

GitRepository: addFile() checks if file exists

GitRepository: fixed hasChanges() (see czproject#25)

Result of hasChanges() was depend on user locale.

IGit: fixed PhpDoc

GitRepository: added method execute()

GitRepository: hasChanges() calls `git update-index -q --refresh`

See czproject#17