ProofGeneral: makes the dependency on TeXLive optional

And fixes the default value of $PGHOME

pkgs/applications/editors/emacs-modes/proofgeneral/4.3pre.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, emacs, texinfo, texLive, perl, which, automake }:
+{ stdenv, fetchurl, emacs, texinfo, texLive, perl, which, automake, enableDoc ? false }:
 
 stdenv.mkDerivation (rec {
   name = "ProofGeneral-4.3pre131011";
@@ -10,7 +10,7 @@ stdenv.mkDerivation (rec {
 
   sourceRoot = name;
 
-  buildInputs = [ emacs texinfo texLive perl which ];
+  buildInputs = [ emacs texinfo perl which ] ++ stdenv.lib.optional enableDoc texLive;
 
   prePatch =
     '' sed -i "Makefile" \
@@ -25,15 +25,20 @@ stdenv.mkDerivation (rec {
        sed -i '96d' doc/ProofGeneral.texi
     '';
 
+  patches = [ ./pg.patch ];
+
   preBuild = ''
     make clean;
   '';
 
   installPhase =
+    if enableDoc
+    then
     # Copy `texinfo.tex' in the right place so that `texi2pdf' works.
     '' cp -v "${automake}/share/"automake-*/texinfo.tex doc
        make install install-doc
-    '';
+    ''
+    else "make install";
 
   meta = {
     description = "Proof General, an Emacs front-end for proof assistants";

pkgs/applications/editors/emacs-modes/proofgeneral/pg.patch

@@ -0,0 +1,16 @@
+diff -r c7d8bfff4c0a bin/proofgeneral
+--- a/bin/proofgeneral	Sat Sep 27 02:25:15 2014 +0100
++++ b/bin/proofgeneral	Sat Sep 27 02:28:16 2014 +0100
+@@ -73,11 +73,7 @@
+ 
+ # Try to find Proof General directory
+ if [ -z "$PGHOME" ] || [ ! -d "$PGHOME" ]; then
+-    # default relative to this script, otherwise PGHOMEDEFAULT
+-    MYDIR="`readlink --canonicalize "$0" | sed -ne 's,/bin/proofgeneral$,,p'`"
+-    if [ -d "$MYDIR" ]; then
+-	PGHOME="$MYDIR"
+-    elif [ -d "$PGHOMEDEFAULT" ]; then
++    if [ -d "$PGHOMEDEFAULT" ]; then
+ 	PGHOME="$PGHOMEDEFAULT"
+     else
+ 	echo "Cannot find the Proof General lisp files: Set PGHOME or use --pghome."