[project @ 2000-06-12 11:04:12 by simonmar]

Fix a nasty bug: the 'c' component of StgUnion was declared as type
StgChar, which sounds reasonable, but meant that when assigning a char
to R1 gcc would correctly arrange to only overwrite the low byte
rather than zero-extending the value.  We assume elsewhere that when
R1 contains a char that the upper 24 bits are zero, so this was wrong.

This bug must have been around for a *long* time, strange that it only
just showed up. <shrug>