Log Message:
update to 1.8
changes:
- Updated for current autoconf/gcc build environment.
- Some uninitialized memory references were found by 'valgrind'.
- Slightly improved writeout/commit performance.
- Explicitly yields to other threads during long running RVM operations.
- More portable detection of fdatasync availability.
- Some more memory initialization fixes, and passing an actual iov
  struct to readv/writev instead of something that looks like it.