BUILD RPM: revert dist token in Release tag, reset dist to nil when building src.rpm
BUILD: support new automake

new automake requires subdirs-object directive, to resolve this:

09:43:37 automake: warning: possible forward-incompatibility.
09:43:37 automake: At least a source file is in a subdirectory, but the 'subdir-objects'
09:43:37 automake: automake option hasn't been enabled.  For now, the corresponding output
09:43:37 automake: object file(s) will be placed in the top-level directory.  However,
09:43:37 automake: this behaviour will change in future Automake versions: they will
09:43:37 automake: unconditionally cause object files to be placed in the same subdirectory
09:43:37 automake: of the corresponding sources.
09:43:37 automake: You are advised to start using 'subdir-objects' option throughout your
09:43:37 automake: project, to avoid future incompatibilities.
09:43:37 tools/otfmerge/Makefile.common:13: warning: source file '$(OTFMERGESRCDIR)/otfmerge.c' is in a subdirectory,
09:43:37 tools/otfmerge/Makefile.common:13: but option 'subdir-objects' is disabled

cmr=v1.8.2:reviewer=ompi-rm1.8