Implement gc of string only hash entries (note, doesn't work likely because a buffer overrun in var expand). Allocate all character data as atomic.

[SVN r35036]

tools/build

@@ -1 +1 @@
-Subproject commit efdbfe6adf13c87321d32f4140e7c97ac9b0590f
+Subproject commit 91c713cc1a83ae2e4fff09c3a8b2bc12fb4f1043