egrep is obsolescent

While running pgperltidy just now on my recently-updated
Linux workstation, I got

$ src/tools/pgindent/pgperltidy .
egrep: warning: egrep is obsolescent; using grep -E

OK, that's a bit in-your-face, but it's not inaccurate.
AFAICT, "egrep" has never been in POSIX, while "grep -E"
has been there at least since POSIX 2008.

So I propose the attached patch, which is just s/egrep/grep -E/g.

I did not touch the two usages in port/aix/mkldexport.sh, though.
I'm not sure what the standardization situation is in AIX, and
this warning doesn't seem like something they'd do anyway.

There is also a reference in configure, which is not a problem
because it tries "grep -E" first.

			regards, tom lane