lkairies-volume-quota/interface: Added ENOSPC to POSIX error types.
lkairies-volume-quota/servers: Added getVolumeQuota() method to StorageManager and VolumeInfo.
lkairies-volume-quota/servers: Added quota check to open operation.
lkairies-volume-quota/servers: Added quota to system attributes and re-implemented get- and setVolumeQuota() methods.
lkairies-volume-quota/servers: Extended quota check for quotas equals 0, i.e. no quota is set.
lkairies-volume-quota/tests: Added quota test.
client: skip immutable attributes in fuse_adapter to avoid errors while copying files on OS X (Issue #312)
client: Added ENOSPC error conversion to fuse_adapter.
tests: Add TRAVIS CI

Add TRAVIS CI config (.travis.yml) and script (contrib/unit_tests.sh) for
executing cpp and java unit tests.
tests: removed C++ unittests (temporarily) from Travis-CI
interface: Added quota to Volume message.
servers: Added quota to CreateVolumeOperation.
client: Added quota to createVolume.
client: Added quota to mkfs.xtreemfs.
client: eliminated compiler warning
Added check for clang compiler to Makefile
flease: create test directory before running FleaseStageTest
flease: create test directory before FleaseAcceptorTest and FleaseProposerTest
tests: repeat JUnit tests three times before failing
client: Added quota to xtfsutil.