Another portability fix: Only include stdbool.h if we actually have it.
Another portability fix: Only include stdbool.h if we actually have it.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb