Patch: Qinghui Xu
This closes#1898
In some environment, the file system only has second accuracy on
file modification timestamp, so delay of 0.1 second before
recompiling could makes the modification timestamp unchanged.
Deploy headers needed to build plugins
Restructure source tree to match lib and to make sure headers are
deployed to INCLUDE_DIR/thrift.
This closes#368 and closes#1039
Client: Compiler
Patch: Nobuaki Sukegawa, rebased by dtmuller
Also fixed by dtmuller:
* Add plugin namespace for erlang language binding
* Fix unit test test_const_value
* Don't clear type cache with every t_program conversion
* Type "wb" may not be supported by popen on non-Windows platforms
* Fix constness of AST type signatures