Avoid file name clash if "$main"-fl.tex already exists.

It's unlikely, but let's be safe and keep the temporary files outside the
checkout to avoid name clash.

git-latexdiff

@@ -466,22 +466,22 @@ if test "$flatten" = 1; then
     (
 	cd old/"$maindir" &&
 	latexpand "$mainbase".tex "${latexpand[@]}" $oldbbl
-    ) > old/"$mainbase"-fl.tex \
+    ) > old-"$mainbase"-fl.tex \
 	|| die "latexpand failed for old version"
     (
 	cd new/"$maindir" &&
 	latexpand "$mainbase".tex "${latexpand[@]}" $newbbl
-    ) > new/"$mainbase"-fl.tex \
+    ) > new-"$mainbase"-fl.tex \
 	|| die "latexpand failed for new version"
     verbose_done
 
-    verbose "Running latexdiff ${latexdiffopt[@]} old/"$mainbase"-fl.tex new/"$mainbase"-fl.tex > ./diff.tex"
-    latexdiff "${latexdiffopt[@]}" old/"$mainbase"-fl.tex new/"$mainbase"-fl.tex > diff.tex \
+    verbose "Running latexdiff ${latexdiffopt[@]} old-${mainbase}-fl.tex new-${mainbase}-fl.tex > ./diff.tex"
+    latexdiff "${latexdiffopt[@]}" old-"$mainbase"-fl.tex new-"$mainbase"-fl.tex > diff.tex \
 	|| die "latexdiff failed"
     verbose_done
 
-    verbose "mv ./diff.tex new/$mainbase-fl.tex"
-    mv -f new/"$mainbase"-fl.tex new/"$mainbase"-fl.tex.orig
+    verbose "mv ./diff.tex new/$main"
+    mv -f new-"$mainbase"-fl.tex new-"$mainbase"-fl.tex.orig
     mv -f diff.tex new/"$main"
     verbose_done
 else