This broke testsuite because it relies on construct
_AX_TEXT_TPL_SUBST([TEST_GEN_FILES_LIST], [.generated_files])
set within configure.ac.

* m4/_ax_text_tpl.m4 (_AX_TEXT_TPL_SUBST): Take optional default
value.

The script generation Makefile snippets are now used from
_ax_text_tpl.m4, DRY principle (the m4 file is maintained
separately for multiple projects).

* configure.ac: Remove all the manual work with substitutions,
start using _AX_TEXT_* macros.
* Makefile.am: Use $(text_tpl_gen*) variables from _ax_text_tpl.
* tests/Makefile.am: Likewise.
* share/postgresql-setup/Makefile.inc: Likewise.
* m4/_ax_text_tpl.m4: New file, TODO: publish somewhere.
* m4/packaging.m4: Reuse _ax_text_tpl.

And add NAME_SERVICE, NAME_PACKAGE and NAME_BINARYBASE on its
place.  This allows packager fine-tune how the files are going to
be generated.

* Makefile.am: Better work with variables.
* .gitignore: Ignore any (generated) service file.
* configure.ac (DISTSUFF): Remove.
(NAME_BIN_PFX, NAME_BIN_SFX, NAME_PKG_PFX, NAME_PKG_SFX)
(NAME_SRV_PFX, NAME_SRV_SFX, NAME_SERVICE, NAME_PACKAGE)
(NAME_BINARYBASE): New variables
* doc/.gitignore: Ignore any man(1) page.
* doc/Makefile.am (HELP2MAN_RUN): Fix the call to work also with
various prefixes/suffixes.
* README.rpm-dist.in: Use new variables.
* legacy-sysv-script.in: Likewise.
* postgresql-setup.in: Likewise.
* m4/packaging.m4 (PGSETUP_SUBST_OPT): New macro, defines,
substitutes and also fixes sed-rules.