THRIFT-646. erlang: Misc build cleanups

THRIFT-646. erlang: Misc build cleanups

- Use AC_ERLANG_PATH_ERLC to find erlc, instead of the generic
  AC_PATH_PROG.
- Also check for erl, just in case it is used internally by checks.
- Use AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR instead of manual hackery to
  find the location where Erlang libraries should be installed.  (This
  doesn't use the discovered version of Erlang, though.  See
  http://lists.gnu.org/archive/html/bug-autoconf/2010-05/msg00003.html .)
- Minor style changes in Makefile.am
- Remove some hacks we were using in the old makefile that were
  necessary because we were not using automake.
- Remove ebin in a "maintainer-clean-local" rule to avoid shadowing the
  default "maintainer-clean" rule which handles MAINTAINERCLEANFILES.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@945744 13f79535-47bb-0310-9956-ffa450edef68