0023197: Draw executable do not detect update of environment variables on Windows.

0023197: Draw executable do not detect update of environment variables on Windows.

New DRAW commands dgetenv and dsetenv are added, allowing to query and set environment variables as defined in C subsystem, from Tcl.

On Windows, special handler is armed in DrawDefaults providing automatic update of C environment when Tcl environment (array env) is modified. Note that this is not needed on Linux (Tcl does this internally).

Fixed problem with "array get env" command.

Added comments to _update_c_env proc.