Fix rez.system is_production_rez_install to handle forward slash paths under windows. (#1899)

This allows to import rez module from paths with forward slashes. The following code printed "False" before the fix:

```
import sys
sys.path.append('C:/rez_test/Lib/site-packages')
from rez.system import system
print( 'is_production_rez_install', system.is_production_rez_install )
```

---------

Signed-off-by: Michal Fratczak <[email protected]>
Signed-off-by: Jean-Christophe Morin <[email protected]>
Co-authored-by: Jean-Christophe Morin <[email protected]>

Author: michalfratczak

src/rez/system.py

@@ -207,6 +207,9 @@ def rez_bin_path(self):
         #
         import rez
         module_path = rez.__path__[0]
+        # Best effort attempt at converting slashes to the current
+        # platform native slash. (for example, forward to backward).
+        module_path = os.path.normpath(module_path)
 
         parts = module_path.split(os.path.sep)
         parts_lower = module_path.lower().split(os.path.sep)