The count() function for STL datatypes returns unsigned, even where it's
only 1/0 result like std::set. Some of the LLVM ADT already return unsigned
count(), while others still return bool count().

In continuation to r197879, this patch modifies DenseMap, DenseSet,
ScopedHashTable, ValueMap:: count() to return size_type instead of bool,
1 instead of true and 0 instead of false.

size_type is typedef-ed locally within each class to size_t.

http://reviews.llvm.org/D4018

Reviewed by dblaikie.