Fix minor bug in setNativeEnabled

The implementation of setNativeEnabled previously had a hard-coded
value of `false`, and ignored the actual value that the caller
passed in.
Add accessors for `nativeEnabled` to ScriptingContainer
Inline Adler32Ext

As an improvement, the new implementation does not rely on reflection
to adjust for a starting checksum. Instead, it uses adler32_combine, as
that computation is reasonably cheap anyhow.

Compared to Adler32Ext, the adjustment is also only performed when a
starting checksum other than the default is provided.
Inline CRC32Ext

Compared to the inlined version of Adler32, this one unfortunately still
relies on reflection for adjusting the starting checksum. This is due
to the fact that crc32_combine is much more expensive, and completely
dominates the runtime up to quite long byte lists.

However, in the event that the reflection trick stops working, we now
fall back to the slower approach, ensuring compatibility with an
unlikely future Java release where the internal CRC32 field name is
changed.

Compared to CRC32Ext, however, neither the reflection nor the slow path
is used when the starting checksum matches the default.
Use CRC-32 table from JZlib
follow changes in pom.xml generation
refactor DateTime#jd
DateTime#jd using 0.5 instead of HALF_DAYS_IN_DAY.to_f
do not unpack jruby-stdlib anymore. cleaned up setup
sync with master
Merge pull request #1807 from k77ch7/refactor_date_time_jd

refactor DateTime#jd
Merge branch 'jruby-1_7' of github.com:jruby/jruby into jruby-1_7
more cleanup and inline comments
fix ArrayJavaProxy#to_a failure on arrays containing null

https://github.com/jruby/jruby/commit/b96b2219f9df6622883a88eda0ae1dbbcb5c2267 added an unprotected method call in a place where the
target could be null. This adds a null check to that expression.
apply enebo's comments on loadService refactor.
Merge pull request #1803 from cprice404/fix-set-native-enabled

Fix minor bug in `setNativeEnabled`, and expose it in ScriptingContainer
Merge pull request #1805 from grddev/zlib-crc-improvements

Zlib crc improvements
Merge branch 'jruby-1_7' of jruby.org:jruby into jruby-1_7
IT to show how many jars with embedded gems can be used right away without any "extra" configuration
allow openssl to work even without native ffi support - fixes #1800