fork while fork

/*
 * hcreate() / hsearch() / hdestroy()
 *
 * SysV/XPG4 hash table functions.
 *
 * Implementation done based on NetBSD manual page and Solaris manual page,
 * plus my own personal experience about how they're supposed to work.
 *
 * I tried to look at Knuth (as cited by the Solaris manual page), but
 * nobody had a copy in the office, so...
 */