Add exclusion for OSX ._<filename> files

Exclude older OSX metadata ._<filename> files from sync, improving
cross-platform sync experience.

Tested-on: arcturus <20 Nov 2013>
Merge pull request #1 from owncloud/master

Merge with owncloud:master
WiP: Attempt to compile without UI
Fix compilation on linux with BUILD_LIBRARIES_ONLY
In case of error, report the right error instead of missing etag

also, missing etag is not a fatal error
Fix compilation without the BUILD_ONLY_LIBRARIES mode
An abort on the reply is not usually a password error.

Copy the code from HTTPCredidentials
Propagator: Add makeConflictFileName function
Propagator: Add support for CSYNC_CONFLICT_FILE_USERNAME
Updater: Ignore files matching with CSYNC_CONFLICT_FILE_USERNAME
Fix function signature: pass argument by const reference
CMake: Find libraries also on Win host compile
Add EXPORT macro to owncloudsync library

Not all the class are exported currently, only the one that seems to be used
by the command line tools
Missing EXPORT
Csync: Add hook for checking if a file is in use already
Csync: Plug code for csync_file_locked_or_open
Csync: Set error at correct place
Add missing line break
Add a compile option to not blacklist error code 5xx
Merge remote-tracking branch 'origin/libowncloudsync_noqtgui'