Return null correctly from MutablePropertySources#get

Prior to this commit, MutablePropertySources#get(String) would throw
IndexArrayOutOfBoundsException if the named property source does not
actually exist. This is a violation of the PropertySource#get contract
as described in its Javadoc.

The implementation now correctly checks for the existence of the named
property source, returning null if non-existent and otherwise returning
the associated PropertySource.

Other changes

 - Rename PropertySourcesTests => MutablePropertySourcesTests
 - Polish MutablePropertySourcesTests for style, formatting
 - Refactor MutablePropertySources for consistency

Issue: SPR-9179
Fix typo in ApplicationContext reference doc

 - Add missing '=' sign in sample code for section 4.2.3

Issue: SPR-8856
Fix typo in spring:eval taglib reference doc

 - Replace 'javascriptEncoding' with 'javaScriptEscape'

Issue: SPR-9188
Merge pull request #46 from pkan/master

* pkan/master:
  Fix typo in spring:eval taglib reference doc
  Fix typo in ApplicationContext reference doc
Remove note on singleton-scoped proxy raising BCE

Before this change bean scopes chapter in Spring reference documentation
had a note which mentioned that creating a scoped proxy for singleton-
or prototype-scoped beans will throw BeanCreationException.

This is no longer the case and this change removes the mentioned note.

Issue: SPR-7940
Merge pull request #45 from sslavic/SPR-7940

* SPR-7940:
  Remove note on singleton-scoped proxy raising BCE
Fix typo in Eclipse import instructions
Merge pull request #44 from mjkrumlauf/patch-1

* patch-1:
  Fix typo in Eclipse import instructions
Fix MultipartResolver javadoc implementation refs

Before this fix MultipartResolver javadoc mentioned that there is only
one concrete implementation included in Spring. This was true as of
Spring 2.5 but Spring 3.1 added another one, Servlet 3.0 Part API based
implementation.

This fix changes MultipartResolver javadoc so that the other one,
StandardServletMultipartResolver implementation, gets also listed.
Changed javadoc mentions also as of which version does Spring bundle
two MultipartResolver implementations.

Issue: SPR-5984
Merge pull request #48 from sslavic/SPR-5984
Generate bracketless tag id in FreeMarker forms

Before this change if FreeMarker Spring form macro was bound to a path
which contains square brackets, those brackets would also appear in id
of generated tag, making the id invalid.

As of this fix all FreeMarker Spring form macros generate tag with id
that does not contain square brackets.

Issue: SPR-8732
Merge pull request #50 from sslavic/SPR-8732
Move QueryTimeoutException to spring-tx

This change fixes a mistake made during an earlier sync with the 3.1.x
branch in which the new QueryTimeoutException class was accidentally
placed in spring-transaction instead of spring-tx.

Issue: SPR-7680
Fix typo in @ComponentScan Javadoc

With thanks to @abdull for pull request #55
Support automatic Hibernate dialect detection

Use the preferred SessionFactoryImplementor#getDialect call as
opposed to the previous Dialect#getDialect approach which required
explicitly setting the 'hibernate.dialect' property.

Issue: SPR-7396
Fix warnings in LocalSessionFactoryBean
Use configured encoding during JiBX unmarshalling

Before this change JibxMarshaller did not use the configured encoding
when unmarshalling XML. This caused issues when content being
unmarshalled was not encoded using the default encoding.

This commit fixes the issue by passing configured encoding to JiBX so
it gets used when unmarshalling instead of the default encoding.

Issue: SPR-7865
Merge pull request #58 from sslavic/SPR-7865

* SPR-7865:
  Use configured encoding during JiBX unmarshalling