* automake.in (&handle_configure): Use the config.status 2.50

* automake.in (&handle_configure): Use the config.status 2.50
invocation syntax for config files and headers.
autoheader needs the name of the file to create, not from what it
must be created, hence CONFIG_HEADER_FULL is $one_name, not
$one_fullname.
* lib/am/configure.am, lib/am/remake-hdr.am: Likewise.
* tests/confsub.test (SUBDIRS): Adjust to the new config.status
invocation.
Strengthen: Use the non-default config.hin source.
Strengthen: Make sure config.h is properly updated when config.hin
is changed.