Input Constraints for Arabic Function

For 5.19.2 ARABIC: Remove from Portable Constraints: X must contain at least one Roman numeral, and only contain Roman numerals. Add Constraint: X must only contain Roman numerals, or an empty string. In Semantics: Remove the sentence The symbols V, L and D may not be followed by a symbol of greater or equal value. Change The following identity holds ... to The following identity shall hold ... Add: If X is an empty string, 0 is returned. [rationale for empty string: that is what ROMAN produces for 0] For 5.19.17 ROMAN: Change Portable Constraint from N>=1 to N>=0 In Semantics: Add: If N is 0, an empty string is returned. [rationale: Excel, Gnumeric, OOo and KSpread return an empty string for 0] Change The following identity holds ... to The following identity shall hold ...