Update version-checking code and list of switches. Delete obsolete
quasi-support for using GNU indent. Remove a lot of no-longer-needed
workarounds for bugs of the old version, and improve comments for
the hacks that remain. Update run_build() subroutine to fetch the
pg_bsd_indent code from the newly established git repo for it.
In passing, fix pgindent to not overwrite files that require no changes;
this makes it a bit more friendly to run on a built tree.
Adjust relevant documentation.
Remove indent.bsd.patch; it's not relevant anymore (and was obsolete
long ago anyway). Likewise remove pgcppindent, since we're no longer
in the business of shipping C++ code.
Piotr Stefaniak is responsible for most of the algorithmic changes
to the pgindent script; I did the rest.
Discussion: https://postgr.es/m/E1dAmxK-0006EE-1r@gemulon.postgresql.org
Discussion: https://postgr.es/m/30527.1495162840@sss.pgh.pa.us
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