Revision 540600

Update to 5.0.0-alpha15

While I'm here, let's clean up the port a bit:
- Switch to MASTER_SITES from USE_GITHUB as suggested by upstream.
- Fix a typo in ALL_TARGET.
- Remove do-build. The ports framework does the right thing already.

PR:		247260
Submitted by:	Martin Filla <freebsd@sysctl.cz>