Documentation for new isc_info_xxx calls

doc/sql.extensions/README.isc_info_xxx

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+New information items
+
+Author:
+	Vlad Horsun <hvlad at users.sourceforge.net>
+
+New item for isc_database_info
+
+isc_info_active_tran_count : 
+	return number of currently active transactions
+
+New item for isc_transaction_info enhancements:
+	
+1. isc_info_tra_oldest_interesting :
+	return number of oldest interesting transaction when current
+	transaction started. For snapshot transactions this is also the 
+	number of oldest transaction in the private TIP copy
+
+2. isc_info_tra_oldest_active
+	for read-committed transaction return number of current transaction 
+	for other transactions return number of oldest active transaction 
+	when current transaction started  
+
+3. isc_info_tra_oldest_snapshot
+	return minimum number of tra_oldest_active of all active transactions
+	when current transaction started. 
+	This value is used as garbage collection threshold
+
+4. isc_info_tra_isolation
+	return transaction isolation mode of current transaction. 
+	format of returned clumplets is following:
+	
+	isc_info_tra_isolation, 
+		1, isc_info_tra_consistency | isc_info_tra_concurrency
+	|
+		2, isc_info_tra_read_committed, 
+			 isc_info_tra_no_rec_version | isc_info_tra_rec_version
+	
+	i.e. for read committed transactions returned 2 items while for 
+	other transactions returned 1 item
+
+5. isc_info_tra_access
+	return read-write access mode of current transaction.
+	format of returned clumplets is following:
+	
+	isc_info_tra_access, 1, isc_info_tra_readonly | isc_info_tra_readwrite
+
+6. isc_info_tra_lock_timeout
+	return lock timeout of current transaction