Fix runtime initialization of immutable associative arrays

An immutable valuable is only modifiable inside of a constructor.
Even inside a constructor it can be modified only one time.
The correct way to modify an immutable associative array is to
freely modify a temporary and then assign it to the immutable.

See also
 - http://dlang.org/hash-map.html
 - https://issues.dlang.org/show_bug.cgi?id=12749
 - http://forum.dlang.org/thread/tigvenrazuwgvxcaescy@forum.dlang.org
Same as commit 1165b8be7d790943a215fcf364da30f098392a2a
Merge pull request #90 from joichiro/2.067

Update project to compile with DMD version 2.067