Change Unicode implicit TRIM semantics

Strings are implicitly trimmed of trailing spaces so that a comparison between two strings fields of different length can be made without trimming them.

It appears that when trim was implemented for unicode strings both spaces and other whitespace characters were treated as not significant.  While that might be useful sometimes, only spaces should be trimmed to address the original issue.

Therefore, the implicit trim semantics for unicode strings will be changed to only remove spaces, but an option (?WHITESPACE) will be added to the TRIM operator for both strings and unicode, which removes all whitespace.