support for partial cleanup of generated files

This is needed for viewers like evince that do not work when the file
being viewed is deleted right after the viewer is launched.

Based on patch from Sebastian Hofer <sebastian.hofer@univie.ac.at>

git-latexdiff

@@ -56,6 +56,20 @@ Options:
                             (default if -o is not used)
     --pdf-viewer <cmd>    use <cmd> to view the PDF file (default: \$PDFVIEWER)
     --no-cleanup          don't cleanup temp dir after running
+    --cleanup MODE	  Cleanup temporary files according to MODE:
+
+                           - keeppdf (default): keep only the
+                                  generated PDF file
+
+                           - none: keep all temporary files
+                                  (may eat your diskspace)
+
+                           - all: erase all generated files.
+                                  Problematic with --view when the
+                                  viewer is e.g. evince, and doesn't
+                                  like when the file being viewed is
+                                  deleted.
+
     --latexmk             use latexmk
     -o <file>, --output <file>
                           copy resulting PDF into <file>
@@ -91,11 +105,17 @@ verbose_done () {
     fi
 }
 
+verbose_say () {
+    if test "$verbose" = 1 ; then
+	printf "%s\n" "$@"
+    fi
+}
+
 old=
 new=
 main=
 view=maybe
-cleanup=1
+cleanup=keeppdf
 verbose=0
 bibtex=0
 biber=0
@@ -126,7 +146,20 @@ while test $# -ne 0; do
 	    PDFVIEWER="$1"
 	    ;;
 	"--no-cleanup")
-	    cleanup=0
+	    cleanup=none
+	    ;;
+        "--cleanup")
+            shift
+            case "$1" in
+                "none"|"all"|"keeppdf")
+                    cleanup="$1"
+                    ;;
+                *)
+                    echo "Bad argument --cleanup $1"
+                    usage
+                    exit 1
+                    ;;
+            esac
             ;;
 	"-o"|"--output")
 	    test $# -gt 1 && shift || die "missing argument for $1"
@@ -331,6 +364,12 @@ if test "$compile_error" = "1" ; then
     exit 1
 fi
 
+if [ -f "$pdffile" ]; then
+    new_pdffile="$tmpdir"/"$pdffile"
+    mv "$pdffile" "$new_pdffile"
+    pdffile="$new_pdffile"
+fi
+
 if test -n "$output" ; then
     abs_pdffile="$PWD/$pdffile"
     (cd "$initial_dir" && cp "$abs_pdffile" "$output")
@@ -341,8 +380,18 @@ if test "$view" = 1  || test "$view" = maybe  && test -z "$output" ; then
     "$PDFVIEWER" "$pdffile"
 fi
 
-if test "$cleanup" = 1 ; then
+case "$cleanup" in
+    "all")
 	verbose "Cleaning-up result"
 	rm -fr "$tmpdir"
 	verbose_done
-fi
+	;;
+    "keeppdf")
+	verbose "Cleaning-up all but pdf (kept in $pdffile)"
+	rm -fr "$tmpdir"/old "$tmpdir"/new "$tmpdir"/diff
+	verbose_done
+	;;
+    "none")
+	verbose_say "Generated files kept in $tmpdir/"
+	;;
+esac