Fix replaceValue for currency smybol replacements

Per http://www.ecma-international.org/ecma-262/5.1/#sec-15.5.4.11, '$$'
must be used to represent a literal '$' in replacement text. This is
because '$' has special meaning - it can be to substitute in parts of a
matched string, for example. This change adds a function for making this
replacement for the currency symbol only.

It appears that this problem could also impact the thousands symbol in
format number, but no language currently supported uses '$' as a symbol
for the thousands delimiter.  Since there is no way to test this and I
want to keep the surface area of this change as small as possible, I've
left out escapes for the thousands delimiter.