Current directory (lodaer.path=.) pathology workaround

It turns out that loader.path=. was pathological and before this
change ended up making the classpath empty (loader.path=.,lib/
would have fixed it). With this change the old behaviour is still
supported, but if the only user-supplied path entry is "." (or
empty) then it is now kept, and translates into the root of the
current archive if running as "java -jar ...".

Fixes gh-270
Disable default configuration detection in @SpringApplicationConfiguration

This is a holding pattern until SPR-11455 is fixed. We now throw an
exception with a helpful message instead of ttrying to detect default
configuration.

Fixes gh-380
Update SpringApplicationContextLoader for Spring 4.0.3

Spring 4.0.3 is not released yet, but we can anticipate the
change. With this commit SpringApplicationContextLoader can discover
default config (nested) classes if none are provided. It should
just work when Spring is upgraded.

Fixes gh-395
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