Inkscape overwrites PYTHONPATH and PATH environment variables

Inkscape (only in Windows!) overwrites PYTHONPATH and PATH environment variables prepending inkscape's own subdirectories. AFIK there is no trivial possibility to use another Python interpreter in windows.

In Windows systems (#ifdef WIN32) Inkscape (since rev 5073) sets PYTHONPATH environment variable hard coded and points (from rev 5073) to inkscape's python subdirectory ignoring the system PYTHONPATH variable,
later (from rev 5106) inkscape's python subdirectory is prepended to a system PYTHONPATH variable (if existing).

(For windows) the PATH variable is also (from rev 5073) hard coded prepending the existing system PATH variable.

http://bazaar.launchpad.net/~inkscape.dev/inkscape/RELEASE_0_91_BRANCH/revision/5073
http://bazaar.launchpad.net/~inkscape.dev/inkscape/RELEASE_0_91_BRANCH/revision/5106

Suggested solutions:

A. do not change the PYTHONPATH and PATH environment variables if existing. This solution has some problems if the system is using a PYTHONPATH pointing to a Python environment not compatible with inkscape's extensions (e.g. inkex.py).

B. let the user configure two environment variables, e.g. INKSCAPE_EXTENSIONS_PYTHONPATH. If this variable exists then use it, otherwise set PYTHONPATH as expected by inkscape. Do the same with INKSCAPE_EXTENSIONS_PATH. This is my preferred solution.

here is a patch for my proposed solution B. Based on RELEASE_0_91_BRANCH rev #13849 of file <inkscape>/src/main.cpp:

542a543,544
> gchar const *inkscape_extensions_pythonpath = g_getenv("INKSCAPE_EXTENSIONS_PATH");
> gchar const *inkscape_extensions_pythonpath = g_getenv("INKSCAPE_EXTENSIONS_PYTHONPATH");
560,563c562,569
< if (path) {
< new_path = g_strdup_printf("%s;%s;%s;%s;%s", exe, python, scripts, perl, path);
< } else {
< new_path = g_strdup_printf("%s;%s;%s;%s", exe, python, scripts, perl);
---
> if (inkscape_extensions_path) {
> new_path = inkscape_extensions_path;
> } else {
> if (path) {
> new_path = g_strdup_printf("%s;%s;%s;%s;%s", exe, python, scripts, perl, path);
> } else {
> new_path = g_strdup_printf("%s;%s;%s;%s", exe, python, scripts, perl);
> }
565,570c571,580
< if (pythonpath) {
< new_pythonpath = g_strdup_printf("%s;%s;%s;%s",
< python_s, pythonlib_s, pythondll_s, pythonpath);
< } else {
< new_pythonpath = g_strdup_printf("%s;%s;%s",
< python_s, pythonlib_s, pythondll_s);
---
> if (inkscape_extensions_pythonpath) {
> new_pythonpath = inkscape_extensions_pythonpath;
> } else {
> if (pythonpath) {
> new_pythonpath = g_strdup_printf("%s;%s;%s;%s",
> python_s, pythonlib_s, pythondll_s, pythonpath);
> } else {
> new_pythonpath = g_strdup_printf("%s;%s;%s",
> python_s, pythonlib_s, pythondll_s);
> }