Rename "parallel recompilation" to "concurrent recompilation".

Also introduced macros for flag aliases for temporary backwards compatibility.

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/23014007

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16280 ce2b1a6d-e550-0410-aec6-3dcde31c8c00