Accumulated fixes for minor issues (#442)

This commit applies various accumulated bugfixes:

- Applied some fixes for compiler warnings based off of the
  following pull requests (with whitespace changes excluded to
  avoid inflating the size of the diff):

  https://github.com/att/ast/pull/281
  https://github.com/att/ast/pull/283
  https://github.com/att/ast/pull/303
  https://github.com/att/ast/pull/304

- clone_type(): Two separate variables in this function share the
  same name. A bugfix from ksh93v- 2013-05-24 was backported to
  avoid conflict issues.

- Backported a minor error message improvement from ksh2020 for
  when the user attempts to run too many coprocesses.

- Backported a ksh2020 bugfix for a file descriptor leak:
  58bc8b56

- Backported ksh2020 bugfixes for unused variable and pointless
  assignment lint warnings:
  47650fe0
  df209c0d
  5e417b00

- Applied a few minor improvements to libast from graphviz:
  e7c03541
  969a7cde

- dtmemory(): Mark unused parameters with NOT_USED(). Based on:
  6ac3ad99

- Applied a few documentation/comment tweaks for the NEWS file,
  printf -v and spawnveg.

- Added a missing regression test for using the rm builtin's -f
  option without additional arguments (this was fixed in
  ksh93u+ 2012-02-14).

src/cmd/ksh93/tests/builtins.sh

@@ -1454,6 +1454,14 @@ if builtin rm 2> /dev/null; then
 	[[ $? == 0 ]] || err_exit 'rm builtin fails to remove non-empty directory and file with -rd options' \
 		"(got $(printf %q "$got"))"
 	[[ -f $tmp/nonemptydir2/shouldexist || -d $tmp/nonemptydir2 ]] && err_exit 'rm builtin fails to remove all folders and files with -rd options'
+
+	# Additional test: 'rm -f' without additional arguments should act
+	# as a no-op command. This bug was fixed in ksh93u+ 2012-02-14.
+	got=$(rm -f 2>&1)
+	if (($? != 0)) || [[ ! -z $got ]]
+	then	err_exit 'rm -f without additional arguments does not work correctly' \
+		"(got $(printf %q "$got"))"
+	fi
 fi
 
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