#42 Fix segfault in the htext widget

[Sergei Golovan]

Hi!

Currently, in BLT 3.0 from Got's HEAD, htext segfaults when I'm trying to select the text inside it. Looks like a typo in its config specs for the selection background (uses BLT_CONFIG_BORDER type instead of BLT_CONFIG_BACKGROUND). The attached patch fixes the segfault.