Hard-coded #E messages make testing hard

[mtorpey]

In package.gi there are various lines that print information when something goes wrong loading a package. They have the form

              Print( "#E  one of the components `Email', `WWWHome', `PostalAddress'\n",
                     "#E  must be bound for each package maintainer\n" );

meaning they can't be switched off in the same way that info warnings can. This makes testing difficult, particularly in the package manager, which wants to test failing packages across various versions of GAP.

Could we use InfoPackageLoading instead? Or perhaps a different info class?

At the very least it would be good if these messages weren't included in ValidatePackageInfo, which after all, is only supposed to be a tool to help PackageInfo.g authors rather than a critical thing on package loading.

[mtorpey]

I just learned about the quiet option to ValidatePackageInfo. This is actually good enough for me! Thanks for adding it.