WSGI: grab DXR_FOLDER from os.environ if not specified in WSGI environ
WSGI: grab DXR_FOLDER from os.environ if not specified in WSGI environ

This makes it easier to pass it in in some cases (e.g. stackato)

jbradberry/dxr,bozzmob/dxr,pelmers/dxr,bozzmob/dxr,jbradberry/dxr,kleintom/dxr,srenatus/dxr,KiemVM/Mozilla--dxr,kleintom/dxr,nrc/dxr,jbradberry/dxr,nrc/dxr,bozzmob/dxr,pelmers/dxr,erikrose/dxr,jbradberry/dxr,jay-z007/dxr,pelmers/dxr,jay-z007/dxr,erikrose/dxr,bozzmob/dxr,pombredanne/dxr,nrc/dxr,gartung/dxr,nrc/dxr,pombredanne/dxr,KiemVM/Mozilla--dxr,KiemVM/Mozilla--dxr,bozzmob/dxr,bozzmob/dxr,pombredanne/dxr,KiemVM/Mozilla--dxr,gartung/dxr,jay-z007/dxr,srenatus/dxr,pombredanne/dxr,gartung/dxr,erikrose/dxr,kleintom/dxr,pombredanne/dxr,jay-z007/dxr,pelmers/dxr,nrc/dxr,gartung/dxr,srenatus/dxr,nrc/dxr,pombredanne/dxr,jbradberry/dxr,srenatus/dxr,gartung/dxr,pelmers/dxr,KiemVM/Mozilla--dxr,kleintom/dxr,jbradberry/dxr,gartung/dxr,pelmers/dxr,kleintom/dxr,bozzmob/dxr,srenatus/dxr,jay-z007/dxr,pelmers/dxr,pombredanne/dxr,gartung/dxr,jbradberry/dxr,jay-z007/dxr,jay-z007/dxr,kleintom/dxr,srenatus/dxr,erikrose/dxr,erikrose/dxr,KiemVM/Mozilla--dxr,kleintom/dxr