[associative.reqmts], [unord.req] Fix typo in precondition for the 'merge' member function. (#1080)

Fixes #919.

Author: jensmaurer

source/containers.tex

@@ -1835,7 +1835,7 @@
 
 \tcode{a.merge(a2)}              &
  \tcode{void}             &
- pre: \tcode{a_eq.get_allocator() == nh.get_allocator()}.\br
+ pre: \tcode{a.get_allocator() == a2.get_allocator()}.\br
  Attempts to extract each element in \tcode{a2} and insert it into \tcode{a}
  using the comparison object of \tcode{a}. In containers with unique keys,
  if there is an element in \tcode{a} with key equivalent to the key of an
@@ -2566,7 +2566,7 @@
 %
 \tcode{a.merge(a2)}              &
  \tcode{void}             &
- Pre: \tcode{a_eq.get_allocator() == nh.get_allocator()}.\br
+ Pre: \tcode{a.get_allocator() == a2.get_allocator()}.\br
  Attempts to extract each element in \tcode{a2} and insert it into \tcode{a}
  using the hash function and key equality predicate of \tcode{a}.
  In containers with unique keys, if there is an element in \tcode{a} with