Fix compiled-in /bin/bash in foomatic filters

Foomatic filters contained a 64-char c string hardcoded to /bin/bash.
This caused some filters (at least pdftops) to fail.

I also had to increase the size of the string because nix paths are too
long.

pkgs/misc/cups/filters.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchurl, pkgconfig, cups, poppler, fontconfig
-, libjpeg, libpng, perl, ijs, qpdf, dbus }:
+, libjpeg, libpng, perl, ijs, qpdf, dbus, bash }:
 
 stdenv.mkDerivation rec {
   name = "cups-filters-${version}";
@@ -34,6 +34,13 @@ stdenv.mkDerivation rec {
       substituteInPlace filter/gstoraster.c --replace execve execvpe
     '';
 
+  patches = [ ./longer-shell-path.patch ];
+
+  postPatch =
+    ''
+      substituteInPlace filter/foomatic-rip/foomaticrip.c --replace "/bin/bash" "${bash}/bin/bash"
+    '';
+
   postInstall =
     ''
       for i in $out/lib/cups/filter/{pstopdf,texttops,imagetops}; do

pkgs/misc/cups/longer-shell-path.patch

@@ -0,0 +1,13 @@
+diff --git a/filter/foomatic-rip/foomaticrip.c b/filter/foomatic-rip/foomaticrip.c
+index 1c019aa..431d2f9 100644
+--- a/filter/foomatic-rip/foomaticrip.c
++++ b/filter/foomatic-rip/foomaticrip.c
+@@ -174,7 +174,7 @@ char cupsfilterpath[PATH_MAX] = "/usr/local/lib/cups/filter:"
+                                 "/opt/cups/filter:"
+                                 "/usr/lib/cups/filter";
+ 
+-char modern_shell[64] = "/bin/bash";
++char modern_shell[128] = "/bin/bash";
+ 
+ void config_set_option(const char *key, const char *value)
+ {