Test for Ilya Perminov's report

Added new test to test-deferred-warnings.script to assess how undefined
variable warnings are handled.
Expand undefined warnings test.
Check for both cases of *compile-file-warnings-behaviour*.
Make the undefined-variables test more portable.
Add test of behaviors when errors are not deferred.

Per query by Ilya Perminov about behavior on SBCL.
Fix typo in name of one configuration variable.
In manual, uniformly use behaviour instead of behavior, for consistency with variable names.
Make the test-undeferred-warnings.script more portable.
Port the undeferred-warnings test to all supported tested implementations.
Break test if lisp-invocation library is not present.

Previously, we would simply skip this test if the lisp-invocation
library was missing, or not sufficiently up-to-date.  Now that the
lisp-invocation library is present as a git submodule, we treat this as
an error condition, instead.
Merge branch 'master' of ssh://common-lisp.net/project/asdf/public_html/asdf
On mkcl, no need to manually load COMPILER anymore, dependency on UIOP provides it properly now.