Turn the warning for uninitialized (result) variables into errors

compiler/lineinfos.nim

@@ -23,6 +23,7 @@ type
     errGeneralParseError,
     errNewSectionExpected,
     errInvalidDirectiveX,
+    errProveInit,
     errGenerated,
     errUser,
     warnCannotOpenFile,
@@ -63,6 +64,7 @@ const
     errGeneralParseError: "general parse error",
     errNewSectionExpected: "new section expected",
     errInvalidDirectiveX: "invalid directive: '$1'",
+    errProveInit: "Cannot prove that '$1' is initialized.",
     errGenerated: "$1",
     errUser: "$1",
     warnCannotOpenFile: "cannot open '$1'",