#107 img::window cannot convert some Tk window paths

[kjnash]

img::window 1.4.13 cannot convert some windows: it requires the Tk window path to begin ".[a-z]". It is correct to exclude upper-case letters, but most other initial characters appear to be valid path names,
e.g. ".[0-9_!&@ ]", and img::window cannot convert these.

[Paul Obermeier]

Fixed with revision 546: https://sourceforge.net/p/tkimg/code/546/