shell.req: removed "function" from "alias|keyword|builtin" check

It seems that our /bin/bash interpreter does not have any "built-in"
functions by default.

$ bash -c 'foo() { :; }; set' |grep ' ()'
foo ()
$ bash -c 'set' |grep ' ()'
$

Thus funcions can be user-defined only.  Generally, what was wrong
with this "function" check is that it was executed in shell.req context.
That is, since e.g. "Info" and "Fatal" are functions within shell.req,
all other dependencies on "Info" and "Fatal" were simply ignored.
This was wrong and this has now been fixed.

Another possibility to ignore current shell.req context while checking
for built-in things is to spawn "clean" shell instance:

-	case "$(type -t -- "$2")" in
+	case "$($sh -c 'type -t "$1"' "$0" "$2")" in

But this can be rather expensive at this early "cleanup" stage.

scripts/shell.req.in

@@ -85,8 +85,7 @@ ShellReq()
 				*) Info "$f: invalid $sh --rpm-requires output: $line"; continue ;;
 			esac
 			case "$(type -t -- "$2")" in
-				# XXX remove "function"?
-				alias|keyword|function|builtin) continue ;;
+				alias|keyword|builtin) continue ;;
 				*) printf '%s\t%s\n' "$1" "$2" ;;
 			esac
 		done