getvar, setvar Error Messages

In Texis version 7 and later, the Vortex getvar and setvar functions (here and here) will issue putmsg messages on certain additional errors: if the variable name is illegal, did not exist at compile time, or is a reserved special variable that cannot be set. These messages allow easier detection of failed calls. The messages may be suppressed with the nomsg flag to getvar or setvar. This behavior change is rolled back if <vxcp compatibilityversion> is set to 6.