support for _Complex is disabled until we figure out the correct
black magic. So instead of using this nice C99 feature, we use the
a strcture with a double type, the same approach that worked pretty
well for the last couple of years.
Switching from one mode to the other is done using the
OPAL_USE_[FLOAT|DOUBLE|LONG_DOUBLE]__COMPLEX macros defined in
opal_datatype_internal.h at line 442.
This commit was SVN r21800.
52c722352d