sanity check for optdepends syntax

only allow optdepends like:
pkgname: description

some (real) examples of invalid optdepends:
 'tcl, python and/or ruby: to use corresponding binding'
 'xorg-fonts-75dpi : X bitmap fonts needed for the interface'
 'ruby-htmlentities (AUR): for one provider named Deastore'
 'xpdf - for pdf'

Signed-off-by: Xavier Chantry <shiningxc@gmail.com>
[Allan: rebase off de39a1f6 and adjust man page]
Signed-off-by: Allan McRae <allan@archlinux.org>
Signed-off-by: Dan McGee <dan@archlinux.org>

doc/PKGBUILD.5.txt

@@ -144,7 +144,7 @@ name. The syntax is: `source=('filename::url')`.
 	base functionality, but may be necessary to make full use of the contents
 	of this package. optdepends are currently for informational purposes only
 	and are not utilized by pacman during dependency resolution. The format
-	should be similar to the following:
+	for specifying optdepends is:
 
 	optdepends=('fakeroot: for makepkg usage as normal user')
 

scripts/makepkg.sh.in

@@ -1180,6 +1180,14 @@ check_sanity() {
 		fi
 	done
 
+	local optdepend
+	for optdepend in "${optdepends[@]}"; do
+		pkg=${optdepend%%:*}
+		if [[ ! $pkg =~ ^[[:alnum:]\>\<\=\.\+\_\-]*$ ]]; then
+			error "$(gettext "Invalid syntax for optdepend : '%s'")" "$optdepend"
+		fi
+	done
+
 	if [ "$install" -a ! -f "$install" ]; then
 		error "$(gettext "Install scriptlet (%s) does not exist.")" "$install"
 		return 1