Add supports for `Group By Clause' as in XQuery 1.1 [1].

[1] http://www.w3.org/TR/xquery-11/#id-group-by
[2] http://www.zorba-xquery.com/doc/zorba-0.9.2/zorba/html/groupby.html

What steps will reproduce the problem?
1. Try with 500 MB xml file.
2. Search for very small data(say 1 KB)

What is the expected output? What do you see instead?
I get "out of memory" even after allotting 512MB of memory to JVM

What version of the product are you using? On what operating system?
i am using xbird-1.0r6-src.zip binary on Windows XP.

Please provide any additional information below.

Can I process xml files of size larger than 1GB using XBird?

Use JDBC to connect to DBMS.

XBird currently passes 91% of the minimal conformance of XQuery Test Suite. 
This success rates should be improved to around 99%.

- XML Query Test Suite
http://www.w3.org/XML/Query/test-suite/

APIs for scripting languages such as ruby, python and php should be provided.

To provide this functionality, it need to be provided XML-RPC interface of
client/server database mode in a similar way to eXist.

What steps will reproduce the problem?
1. Download the jars and war files to local system.
2. Place the bib.xml and query.txt (containing query) at C:\\ drive.
3. Execute the jar from cmd line...java -jar xbird-open-1.0_fat.jar -q 
C:\query.txt.

What is the expected output? What do you see instead?
Query results should be shown from the XML file but it shows an error 
message 'Invalid or corrupt xbird-open-1.0_fat.jar'

What version of the product are you using? On what operating system?
1.0 version of code on Windows XP

Please provide any additional information below.
What is wrong?

Support XQJ API

We have to provide a command for creating indicies for XML documents
adaptically.

Currently, indexing XML documents is enabled only when the following
settings are set on loading XML documents.

* xbird.database.bulkload.buildidx=true
* xbird.database.dtm.use_mmap=false

http://code.google.com/p/xbird/source/browse/trunk/xbird-open/main/conf/xbird/co
nfig/xbird.properties

XBird is currently optimized for read-oriented workloads.
It does not currently accept a node level updates.

Supporting XQuery Update is a considerable option as a future enhancement,
but the priority is low.

  * http://www.w3.org/TR/xquery-update-10/

Compare the performance of XBird to other XQuery engines,  e.g., saxon-b,
qizx/open, basex and monetdb/xquery.

XCheck - A platform for benchmarking XML query processors
http://ilps.science.uva.nl/Resources/XCheck/

XBird is currently optimized for read-oriented workloads.
It does not currently accept a node level updates.

Supporting [http://www.w3.org/TR/xquery-update-10/ XQuery Update] is a
considerable for future enchancement, but currently in low priority.

  * [http://www.w3.org/TR/xquery-update-10/
http://www.w3.org/TR/xquery-update-10/]