don't use substring when doing StringBuffer#append

reduces garbage

h2/src/main/org/h2/expression/Function.java

@@ -2066,7 +2066,7 @@ public class Function extends Expression implements FunctionCall {
                 if (buff == null) {
                     buff = new StringBuilder(size);
                     if (i > 0) {
-                        buff.append(original.substring(0, i));
+                        buff.append(original, 0, i);
                     }
                 }
                 if (index < replaceSize) {

h2/src/main/org/h2/tools/Csv.java

@@ -551,7 +551,7 @@ public class Csv implements SimpleRowSource {
             buff.append(chars[idx + 1]);
             start = idx + 2;
         }
-        buff.append(s.substring(start));
+        buff.append(s, start, s.length());
         return buff.toString();
     }
 

h2/src/main/org/h2/util/StringUtils.java

@@ -583,7 +583,7 @@ public class StringUtils {
             }
             int n = s.indexOf('\n', i);
             n = n < 0 ? s.length() : n + 1;
-            buff.append(s.substring(i, n));
+            buff.append(s, i, n);
             i = n;
         }
         if (newline && !s.endsWith("\n")) {

h2/src/test/org/h2/test/scripts/TestScript.java

@@ -213,7 +213,7 @@ public class TestScript extends TestBase {
                 // do nothing
             } else if (sql.endsWith(";")) {
                 write(sql);
-                buff.append(sql.substring(0, sql.length() - 1));
+                buff.append(sql, 0, sql.length() - 1);
                 sql = buff.toString();
                 buff = new StringBuilder();
                 process(sql);