make context active before clearing buffers
Revert "make context active before clearing buffers"

This reverts commit 636fedff122dc254ec77ea5504cf8d94acd8b351.
Add gcc back to build matrix (fixes #465)
Update Ubuntu instructions in README [skip ci]
fix 64-bit iOS builds
bump Cocoa
bump Cocoa for location fixes
bump Cocoa one more time
Merge branch 'master' into libuv010

Conflicts:
	setup-libraries.sh
bump mapnik-packaging