Fix Issue 12027 - Iterate set bits in BitArray.

Also adds:
- countTrailingZeros(v)
- countBitsSet(v)
- bitsSet(v)

Notes:
- There is a `popcnt` function in `core.bitops`, but it only works with `int`.
- `bitsSet(v)` could be a bidirectional and possibly even random access range, but I'll leave that for future work for now.
Performance improvements for dense BitArray.bitsSet.
Reimplement countTrailingZeros using bsf.
Refine BitArray.init requirements and docuemntation.
std.process: Add workDir parameter
Mark countBitsSet and countTrailingZeroes as private for now
Speed up trie construction by factor of ~3.

Take advantage of word-at-once checking for slices of bit-packed
arrays in the trie.
std.digest.sha: disable SSSE3 for SHA because it has unsupported calling convention
std.format, std.math: workarounds for different behaviour of sprintf
std.conv: workarounds for different behaviour of strtold
std.math: disable unittests for exp2f and exp2l
std.math: fix lrint(real), disable tmpfile test
std.process: seek to end of file before trying to append to it from another process
std.process: do not try to terminate an invalid process handle
win64.mak: disable COMDAT folding for release build
Merge pull request #1411 from rainers/win64_enable_unittests

do not skip unittests for Win64
[Trivial] Fix documentation typos in std.algorithm
[Trivial] Fix documentation typos in std.array
Merge pull request #1973 from yazd/fix-typos

[Trivial] Fix documentation typos
Merge pull request #1969 from blackwhale/faster-trie-build

std.uni - speed up Trie construction by factor of ~3
fix 'jobserver unavailable: using -j1' warning for $(SUBMAKE)

- Problem is that make doesn't recognize $(SUBMAKE) as
  make, so it won't pass MAKEFLAGS and doesn't use it's
  jobserver.

- Fixed by explicitly using $(MAKE) ...

For reference:
http://www.gnu.org/software/make/manual/html_node/Error-Messages.html
http://www.gnu.org/software/make/manual/html_node/MAKE-Variable.html#MAKE-Variable
[Trivial] Fix documentation typos
Merge pull request #1974 from yazd/fix-typos

[Trivial] Fix documentation typos in Phobos
Merge pull request #1901 from Poita/bug12027

Fix Issue 12027 - Iterate set bits in BitArray.
Fix Issue 12245 - BinaryHeap expensive in -debug

https://d.puremagic.com/issues/show_bug.cgi?id=12245
Merge pull request #1976 from Poita/bug12245

Fix Issue 12245 - BinaryHeap expensive in -debug
Merge pull request #1928 from CyberShadow/std-process-cwd

std.process: Add workDir parameter