Implemented a namespace map that allows searching

of namespaces (only in the modules where they've
been found) for entities inside those namespaces.

For each NamespaceDecl that has been imported into
the parser, we maintain a map containing
[ModuleSP, ClangNamespaceDecl] pairs in the ASTImporter.
This map has one entry for each module in which the
namespace has been found.  When we later scan for an
entity inside a namespace, we search only the modules
in which that namespace was found.

Also made a small whitespace fix in 
ClangExpressionParser.cpp.

llvm-svn: 141748