added an active face for the mesh editmode and normal mesh - this is needed because the TFace flag was not always easy to access from editmode.

using the last selected face was almost good enough however when selecting verts and edges the last selected face would become inactive and the space image would flicker about too much.
The active face is used for getting the space image at the moment and keeps scripts that use this flag working also.

This has 2 commands to get and set, so the variable is not accessed directly.

all "UV Calculate" scripts work now

last commit crashed when in solid draw mode, it seems subsurf modifier is ignoring the displayMask since MTFACE is available. just made it do a null check for now.

uvcalc_follow_active_coords.py - should be done inC and put in the snap menu.

source/blender/include/BIF_editmesh.h

@@ -259,4 +259,7 @@ void free_uv_vert_map_EM(UvVertMap *vmap);
 int EM_texFaceCheck(void); /* can we edit UV's for this mesh?*/
 int EM_vertColorCheck(void); /* can we edit colors for this mesh?*/
 
+void EM_set_actFace(struct EditFace *efa);
+struct EditFace * EM_get_actFace(void);
+
 #endif