Counter-intuitive double key press needed to input diacritic characters (instead of regular diacritic+space key combination)

[Alfredo Fernández Díaz]

Fixing ticket #79 introduced this one.

In most languages other than English, some characters are overlaid on regular letters to form "combined" characters, f.e.: ¨ + o = ö through the use of "dead keys". Dead keys are not supposed to produce character output, this should happen only if a valid regular character is typed afterwards, and then a single combined character is produced. The fix for #79 drops all diacritic characters as typed, thus they can't be combined with a space to produce a standalone (non-diacritic) character when one is needed in the standard way all typists are used to.

This defect is minor compared to #79, as the current PM implementation offers a simple yet counter-intuitive workaround: hitting a dead key twice will still type the standalone character, f.e. ⁺ = ^{. Still, this should be fixed.}

Proposed fix: create a 1-char buffer to store diacritic characters as they are entered. The next time a space is typed, check for the right 'combined' flag, and output the last diacritic stored in the buffer instead.