Release 1.15

• switched from mmap based writing to simpler stdio based writing. Has a minor impact (0.5 microseconds) on microbenchmarks for asynchronous writes. Synchronous writes speed up from 30ms to 10ms on linux/ext4.
  Should be much more reliable on diverse platforms.
• compaction errors now immediately put the database into a read-only mode (until it is re-opened). As a downside, a disk going out of space and then space being created will require a re-open to recover from, whereas previously that would happen automatically. On the plus side, many corruption possibilities go away.
• force the DB to enter an error-state so that all future writes fail when a synchronous log write succeeds but the sync fails.
• repair now regenerates sstables that exhibit problems
• fix issue #224 - Use native memory barriers on OSX
• fix issue #218 - QNX build is broken
• fix build on iOS with xcode 5
• make tests compile and pass on windows