Add streq to reduce confusion of !strcmp

I have twice now made the mistake of replacing !strcmp() with !match() or
similiar. The return value of a match()-family function has the opposite
sense of strcmp()-family one. match() functions return 0 to indicate
*no match*, while strcmp() does the opposite. To prevent mistakes of
this nature, and to make it easier to read code using strcmp, the streq
macro was created.
Do MODE permission checks right, and add doc/uirc.txt