Make drrun_exe on Linux use LD_PRELOAD injection by default

This is needed to replace the drrun script.  The injector now reads the
DR's options in the config file to decide if it should use early
injection or LD_PRELOAD injection.  The drrun frontend accepts the
-early argument for compatibility with the script and simply forwards
-early_inject through to DR's options.

Review URL: https://codereview.appspot.com/7313044

git-svn-id: https://dynamorio.googlecode.com/svn/trunk@1891 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6
Merge branch 'master' into drdeploy-ld-preload