Merge pull request #968 from Tribler/devel

Merge devel to next
fix PyDeadObject in SaveAs.py
load libX11.so.6 instead of libX11.so
Merge pull request #970 from LipuFei/fix_pydeadobject_saveas

Fix PyDeadObject in SaveAs.py
Merge pull request #971 from LipuFei/fix_load_libx11

Fix loading libX11.so
fix a logging problem in MetadataCommunity
Merge pull request #974 from LipuFei/fix_metadata_community_log

fix a logging problem in MetadataCommunity
Fix libtorrent big_number issue
Merge pull request #975 from egbertbouman/fix_bignumber

Fix libtorrent big_number issue
reduce TFTP collecting rate
Merge pull request #976 from LipuFei/reduce_tftp_rate

Reduce TFTP collecting rate
increase version number to 6.4.0
Merge pull request #978 from LipuFei/increase_version

Increase version number to 6.4.0
Merge pull request #977 from Tribler/next

Merge next back to devel