Fix python env path prepends in gitbash

Signed-off-by: javrin <jawabiscuit@users.noreply.github.com>

src/rez/data/tests/builds/packages/foo/1.1.0/package.py

@@ -10,7 +10,9 @@
 
 @include("late_utils")
 def commands():
-    env.PYTHONPATH.append('{root}/python')
+    # Test prepends by throwing in an extra python path
+    env.PYTHONPATH.prepend('{root}/python')
+    env.PYTHONPATH.append('{root}/noexist')
     env.FOO_IN_DA_HOUSE = "1"
 
     late_utils.add_eek_var(env)

src/rez/rex.py

@@ -233,7 +233,13 @@ def get_public_methods(self):
             ('undefined', self.undefined)]
 
     def _env_sep(self, name):
-        return self._env_sep_map.get(name, self.interpreter.pathsep)
+        return self.interpreter.env_sep_map.get(
+            name,
+            self._env_sep_map.get(
+                name,
+                self.interpreter.pathsep
+            )
+        )
 
     def _is_verbose(self, command):
         if isinstance(self.verbose, (list, tuple)):
@@ -493,6 +499,12 @@ class ActionInterpreter(object):
     #
     pathsep = os.pathsep
 
+    # Path separator mapping. There are cases (eg gitbash - git for windows) where
+    # the path separator changes based on the variable
+    # (eg "PATH": ":", and "PYTHONPATH": ";")
+    #
+    env_sep_map = {}
+
     # RegEx that captures environment variables (generic form).
     # Extend/override to regex formats that can capture environment formats
     # in other interpreters like shells if needed