input.js: adjust special key handling for non-US keys.

input.js: adjust special key handling for non-US keys.

Issue #21 - non-US keyboard layouts.

Only identify some keys as special during the keyDown event so that
when using non-US keyboards the values don't overlap with the values
for normal keys.

Some keys have to still be identified in both keyDown and keyPress
since they generate both: backspace and enter for Firefox and Opera,
tab for Opera.