Fixed getTypeDifferenceWeight algorithm in ReflectionHelper, and removed unused argsRequiringConversion storage

Issue: SPR-11306
Removed javadoc references to non-accessible subclasses
Turned ArgumentsMatchKind and ArgumentsMatchInfo to package-visible
Removed Commons Lang references
Remove unused import in MockHttpServletRequestBuilderTests
ObjectUtils.isCompatibleWithThrowsClause supports varargs now
Introduced "spring.getenv.ignore" system property for preventing System.getenv calls

Issue: SPR-11297
Polishing
Introduced "globalInitializerClasses" next to the existing "contextInitializerClasses", applying to FrameworkServlets as well

Issue: SPR-11314
Polishing
checkNotModified needs to consider HEAD as well

Issue: SPR-11317
Added tests for context initializers on DispatcherServlet

Issue: SPR-11314
Polishing
Several ref doc fixes

Issue: SPR-8182
Issue: SPR-11243
Issue: SPR-11292
Issue: SPR-11318
Fixed version number in xsd comment
Declared JDK 6 update 18 as minimum requirement
Mentioned "-parameters" compiler flag in javadoc
Fixed accidental use of JDK 1.7+ Integer/Long.compare methods

Issue: SPR-11319
Polishing
Introduced customizeConnection callbacks for URLConnection used by exists() / contentLength() / lastModified()

Issue: SPR-11320