Input validation for codegen flag (#137)
Input validation for codegen flag (#137)

$ ../../bin/fstar.exe --codegen Ocaml
Wrong argument to codegen flag

FStarLang/FStar,MallabaevAzamat/FStar,aa755/FStar,hoheinzollern/FStar,aa755/FStar,MallabaevAzamat/FStar,YaccConstructor/FStar,MallabaevAzamat/FStar,A-Manning/FStar,YaccConstructor/FStar,FStarLang/FStar,hoheinzollern/FStar,hoheinzollern/FStar,msprotz/FStar,A-Manning/FStar,YaccConstructor/FStar,YaccConstructor/FStar,msprotz/FStar,aa755/FStar,A-Manning/FStar,FStarLang/FStar,msprotz/FStar,MallabaevAzamat/FStar,msprotz/FStar,hoheinzollern/FStar,aa755/FStar