Fix size class overflow handling when profiling is enabled.

Fix size class overflow handling for malloc(), posix_memalign(),
memalign(), calloc(), and realloc() when profiling is enabled.

Remove an assertion that erroneously caused arena_sdalloc() to fail when
profiling was enabled.

This resolves #232.
diff --git a/configure.ac b/configure.ac
index bb6f3a3..61adc2a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -513,6 +513,7 @@
   AC_DEFINE_UNQUOTED([JEMALLOC_PREFIX], ["$JEMALLOC_PREFIX"])
   AC_DEFINE_UNQUOTED([JEMALLOC_CPREFIX], ["$JEMALLOC_CPREFIX"])
 fi
+AC_SUBST([JEMALLOC_CPREFIX])
 
 AC_ARG_WITH([export],
   [AS_HELP_STRING([--without-export], [disable exporting jemalloc public APIs])],