Fix 8167 (identity constructor) and 9061 (bitwise ops)
Removed unnecessary allocation and computation
Fixed compilation errors on 64-bit platforms (hopefully)
Merge branch 'master' of https://github.com/D-Programming-Language/phobos

Conflicts:
	std/bigint.d
Got rid of expensive AddOrSubInt call (and related allocation).
Added description of logical (bitwise) operations.
Removed unnecessary allocations in twosComplement call.
Fix name of bitwise operations
Turned Examples section in std.digest.* into documented unittest
Merge pull request #1721 from Biotronic/master

Fix 8167 (BigInt identity constructor) and 9061 (BigInt bitwise ops)
Merge pull request #1780 from Geod24/fix-digest

Turned Examples section in std.digest.* into documented unittest