manual: use consistent terminology

The ksh manual page is one of the few places that calls globbing
"file name generation". The mksh and zsh manuals use the same term.
But every other shell's manual calls it "pathname expansion": bash,
dash, yash, FreeBSD sh. So does ksh's built-in documentation (alias
--man, export --man, readonly --man, set --man, typeset --man).
What's more, the authoritative ksh reference, Bolsky & Korn's 1995
"The New Kornshell" book, also calls it "pathname expansion", and
so does the POSIX standard.

Similarly, "arithmetic substitution" should be called "arithmetic
expansion" per Bolsky & Korn as well as POSIX.

This commit has several other miscellaneous documentation tweaks as
well.

src/cmd/ksh93/DESIGN

@@ -109,7 +109,7 @@ sh directory:
 	5.	deparse.c contains code to generate shell script from
 		a parse tree.
 	6.	expand.c contains code for file name expansion and
-		file name generation.
+		pathname expansion.
 	7.	fault.c contains code for signal processing, trap
 		handling and termination.
 	8.	fcin.c contains code for reading and writing a character