Fix missing rebuilds during `make dist' with BSD make.

Fix missing rebuilds during `make dist' with BSD make.
* automake.in (generate_makefile): Do not push Makefile.in, and
Makefile.am into DIST_COMMON here.
* lib/am/configure.am (DIST_COMMON): Do it here, and use
%MAKEFILE-AM% and %MAKEFILE-IN% so that items in DIST_COMMON
actually match the targets.   Prefix `configure' with `$(srcdir)/'
to match the target.
* tests/remake4.test: New file.
* tests/Makefile.am (TESTS): Add remake4.test.
Report from Akim Demaille.