Add pg_string_endswith as the start of a string helper library in src/common.

Backpatch to 9.3 where src/common was introduce, because a bugfix that
needs to be backpatched, requires the function. Earlier branches will
have to duplicate the code.

src/common/Makefile

@@ -23,7 +23,7 @@ include $(top_builddir)/src/Makefile.global
 override CPPFLAGS := -DFRONTEND $(CPPFLAGS)
 LIBS += $(PTHREAD_LIBS)
 
-OBJS_COMMON = exec.o pgfnames.o psprintf.o relpath.o rmtree.o username.o wait_error.o
+OBJS_COMMON = exec.o pgfnames.o psprintf.o relpath.o rmtree.o string.o username.o wait_error.o
 
 OBJS_FRONTEND = $(OBJS_COMMON) fe_memutils.o
 

src/common/string.c

@@ -0,0 +1,43 @@
+/*-------------------------------------------------------------------------
+ *
+ * string.c
+ *		string handling helpers
+ *
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/common/string.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+
+#ifndef FRONTEND
+#include "postgres.h"
+#else
+#include "postgres_fe.h"
+#endif
+
+#include "common/string.h"
+
+
+/*
+ * Returns whether the string `str' has the postfix `end'.
+ */
+bool
+pg_str_endswith(const char *str, const char *end)
+{
+	size_t		slen = strlen(str);
+	size_t		elen = strlen(end);
+
+	/* can't be a postfix if longer */
+	if (elen > slen)
+		return false;
+
+	/* compare the end of the strings */
+	str += slen - elen;
+	return strcmp(str, end) == 0;
+}