Add GC benchmarks.

gc-benchmarks/string.scm

@@ -0,0 +1,25 @@
+;;; From from http://www.ccs.neu.edu/home/will/Twobit/KVW/string.txt .
+; string test
+; (try 100000)
+
+(define s "abcdef")
+
+(define (grow)
+	(set! s (string-append "123" s "456" s "789"))
+	(set! s (string-append
+		(substring s (quotient (string-length s) 2) (string-length s))
+		(substring s 0 (+ 1 (quotient (string-length s) 2)))))
+	s)
+
+(define (trial n)
+	(do ((i 0 (+ i 1)))
+		((> (string-length s) n) (string-length s))
+		(grow)))
+
+(define (try n)
+	(do ((i 0 (+ i 1)))
+		((>= i 10) (string-length s))
+		(set! s "abcdef")
+		(trial n)))
+
+(try 50000000)