The following should unlock a locked working copy (tested on svn client version 1.6.11 and elipse version: Mars.2 Release (4.5.2))
step 1: (go to working copy directory) $cd working_copy_dir
step 2: (connect to svn sqlite database) $sqlite3 .svn/wc.db
step 3: (delete all records from table WC_LOCK) sqlite> delete from WC_LOCK;
step 4: (disconnect from sqlite 3 database) sqlite>ctrl + d
step 5: (from eclipse) right click on your working copy, then click Team -> Refresh/Cleanup