Fix for <https://nvd.nist.gov/vuln/detail?vulnId=CVE-2015-8327>.

--- a/util.c	2014-06-20 19:26:18 +0000
+++ b/util.c	2015-10-30 15:45:03 +0000
@@ -31,7 +31,7 @@
 #include <assert.h>
 
 
-const char* shellescapes = "|<>&!$\'\"#*?()[]{}";
+const char* shellescapes = "|<>&!$\'\"`#*?()[]{}";
 
 const char * temp_dir()
 {