[MONDRIAN-1471]  Switched RolapSchemaReader.getMemberReader() from being synchronized at the method level to using a double-checked lock instead.  getMemberReader() is called frequently inside of nested loops;
this approach should reduce some amount of thread contention.
[MONDRIAN-1471] Added javadoc.
Merge pull request #88 from mkambol/mondrian-1471

[MONDRIAN-1471]  Switched RolapSchemaReader.getMemberReader() from being...