Fixed broken test: now verifying that an attempt to set a null active profile throws an IllegalArgumentException.

Add Import-Template entry for org.spring-framework.jndi

Issue: SPR-8038

Issue: SPR-8038, SPR-8545, SPR-8490

Prior to this change, StandardServletEnvironment evaluated a
"jndiPropertySourceEnabled" flag to determine whether or not to add a
JndiPropertySource.  Following the changes introduced in SPR-8490, there
is now no reason not to enable a JNDI property source by default. This
change eliminates the support for "jndiPropertySourceEnabled" and adds
a JndiPropertySource automatically.

Issue: SPR-8545, SPR-8490

Provides a convenient mechanism for activating an additional profile
while preserving those that are already active, as opposed to
calling #setActiveProfiles with the contents of #getActiveProfiles plus
the new profile.

Issue: SPR-8548

Consolidates validation for profiles and provides a mechanism for
AbstractEnvironment subclasses to customize validation logic if
desired.

Issue: SPR-8482

RequiredAnnotationBeanPostProcessor's skip attribute accepts "true" as String value as well (SPR-8617)