Fix buffer overflows in shortcut and workspace name handling
The handling of user defined shortcuts was not checking the length
of the shortcut before copying it to a fixed-length temporary buffer,
char buf[128];
strcpy(buf, shortcutDefinition);
and strcpy() is well known for not checking if overflows will occur.
In particular, wmaker was crashing here if a big 'shortcut' was defined
either through WPrefs or by directly editing the configuration files.
This is now avoided by using strncpy() instead.
And this patch also fixes a similar buffer overflow for big workspace
names too.
Furthermore, use MAX_SHORTCUT_LENGTH instead of raw number and define
it to be 32 instead of 128.