valgrind: Add a suppression for a hunspell memory leak during the SpellCheckStrings_EN_US test

tools/valgrind/memcheck/suppressions.txt

Index: tools/valgrind/memcheck/suppressions.txt
===================================================================
--- tools/valgrind/memcheck/suppressions.txt	(revision 22262)
+++ tools/valgrind/memcheck/suppressions.txt	(working copy)
@@ -997,3 +997,22 @@
   fun:_ZN7testing8UnitTest3RunEv
   fun:main
 }
+{
+  bug_18254b
+  Memcheck:Leak
+  fun:_Znaj
+  fun:_ZN8AffixMgr10parse_fileEv
+  fun:_ZN8AffixMgrC1EPN8hunspell11BDictReaderEPP7HashMgrPi
+  fun:_ZN8HunspellC1EPKhj
+  fun:_ZN12SpellChecker10InitializeEv
+  fun:_ZN12SpellChecker14SpellCheckWordEPKwiPiS2_PSt6vectorISbIwSt11char_traitsIwESaIwEESaIS7_EE
+  fun:_ZN43SpellCheckTest_SpellCheckStrings_EN_US_Test8TestBodyEv
+  fun:_ZN7testing4Test3RunEv
+  fun:_ZN7testing8internal12TestInfoImpl3RunEv
+  fun:_ZN7testing8internal12TestInfoImpl7RunTestEPNS_8TestInfoE
+  fun:_ZN7testing8TestCase3RunEv
+  fun:_ZN7testing8TestCase11RunTestCaseEPS0_
+  fun:_ZN7testing8internal12UnitTestImpl11RunAllTestsEv
+  fun:_ZN7testing8UnitTest3RunEv
+  fun:main
+}