Add a HACKING file.
actually build memoryerror.d
simplify unittest for critical region
improve critical regions

- use a fine grained mutex to negotiate critical regions
  and thread suspension

- we no longer have to suspend & resume a thread
  that is in a critical region
Thread.suspend must now be synchronous

So remove the comments about a possible different implementation
and actually check for sem_wait failure.
eagerly allocate Thread locks
exponentially increase wait time up to 10ms
simplify loop
Merge pull request #498 from dawgfoto/cleanupGC

simplify loop
enable docs for critical regions
Merge pull request #499 from dawgfoto/criticalRegion

improve critical region
Merge pull request #494 from alexrp/hacking

Add a HACKING file.
Add Linux/PPC64 values to core.sys.posix.fcntl.

Simply adds the missing values.
Merge pull request #502 from redstar/ppc_fcntl

Add Linux/PPC64 values to core.sys.posix.fcntl.
Add ucontext_t on Linux/PPC64.

Adds the required data structures for ucontext_t.
Merge pull request #503 from redstar/ppc_ucontext

Add ucontext_t on Linux/PPC64.
Fix O_RSYNC value on Linux/PPC64
Merge pull request #504 from redstar/ppc_fcntl

Fix O_RSYNC value on Linux/PPC64
Implement review comments to ucontext on Linux/PPC64
use backslash