* lib/m4sugar/m4sugar.m4 (m4_init): Merge the two m4_wrap
calls, so that we do not care whether they are LIFO or FIFO;
in the m4_wrap, do not check which diversion is the topmost
one, just check that the stack is balanced at the end.
* lib/m4sugar/m4sh.m4 (AS_INIT): We are going to change the
base diversion forever--pop the previous diversion before
opening the new one; consequently, remove the m4_wrap call.
* lib/autotest/general.m4 (AT_INIT): Likewise.
* tests/m4sugar.at: Do not use
m4_wrap([m4_diversion_pop([..])]), for educational purposes.