.gitignore: Simplify references to the same file in different directories

Unless a .gitignore pattern is anchored, it'll match in any directory, not juts at the top level.  Simplify .gitignore accordingly.
Merge pull request #3193 from joshtriplett/patch-1

.gitignore: Simplify references to the same file in different directories
Refactor: CTxMempool class to its own txmempool.{cpp,h}
Merge pull request #3154 from gavinandresen/mempool_refactor

Mempool refactor
Added src/test CMakeFile.txt for unit testing. (still needs work)
Fixed versioning and inlined sources files instead of globbed.
Merge remote-tracking branch 'upstream/master'
+src/txmempool.*