Add nothrow for thread_detachThis
Sync gc_* declrations with core.memory

The forward gc_enable, gc_disable, gc_malloc delcarations in core.thread should
be nothrow as defined in core.memory.
Merge pull request #1064 from dsp/master

Add nothrow for thread_detachThis
Merge pull request #1065 from dsp/fix-import

Sync gc_* declrations with core.memory
cleanup old declarations and import core.memory
put a D in the C
Merge pull request #1067 from MartinNowak/typo

put a D in the C
Merge pull request #1066 from MartinNowak/gcDecls

cleanup old declarations and import core.memory