Don't save "warning: " prefix in lastwarn() message. * error.cc (vwarning): Save base_msg (without "warning: ") to Vlast_warning_message. * error.cc (error_1): Use std::string operators rather than strsave to strip "\n" from fmt string. Simpler syntax avoids having to delete [] memory created with new. * error.cc (warning_1): Strip trailing newline from fmt string as error_1 does. * fail.m: Fix input validation which allowed nonsensical second input with 3 args. Don't post-process warning or error messages from lastwarn or lasterr. Add BIST test for input validation.

header = '{date|shortdate}  {author|person}  <{author|email}>\n\n'
changeset = '\t{desc|tabindent|strip}\n\n\tFiles: {files|stringify|fill68|tabindent|strip}\n\n'