add a feature option for non-strict function 'caller' property, add a feature option to disable Array.splice() real world behavior, document the two options

Makefile

@@ -172,6 +172,8 @@ CCOPTS_SHARED += -DDUK_OPT_DEBUG_BUFSIZE=512
 #CCOPTS_SHARED += -DDUK_OPT_NO_INTERRUPT_COUNTER
 #CCOPTS_SHARED += -DDUK_OPT_NO_JSONX
 #CCOPTS_SHARED += -DDUK_OPT_NO_JSONC
+#CCOPTS_SHARED += -DDUK_OPT_FUNC_NONSTD_CALLER_PROPERTY
+#CCOPTS_SHARED += -DDUK_OPT_NO_ARRAY_SPLICE_NONSTD_DELCOUNT
 #CCOPTS_SHARED += -DDUK_CMDLINE_BAREBONES
 CCOPTS_NONDEBUG = $(CCOPTS_SHARED) -Os -fomit-frame-pointer
 CCOPTS_NONDEBUG += -g -ggdb

src/duk_features.h

@@ -1632,6 +1632,17 @@ typedef FILE duk_file;
  * when deleteCount is omitted.
  */
 #define DUK_USE_ARRAY_SPLICE_NONSTD_DELCOUNT
+#if defined(DUK_OPT_NO_ARRAY_SPLICE_NONSTD_DELCOUNT)
+#undef DUK_USE_ARRAY_SPLICE_NONSTD_DELCOUNT
+#endif
+
+/* Non-standard 'caller' property for function instances, see
+ * test-bi-function-nonstd-caller-prop.js.
+ */
+#undef DUK_USE_FUNC_NONSTD_CALLER_PROPERTY
+#if defined(DUK_OPT_FUNC_NONSTD_CALLER_PROPERTY)
+#define DUK_USE_FUNC_NONSTD_CALLER_PROPERTY
+#endif
 
 /*
  *  Function instance features.

website/guide/compiling.html

@@ -176,6 +176,24 @@ The table below summarizes the available options, in no particular order:</p>
     declarations ("hoist" them to function top) with V8-like semantics.</td>
 </tr>
 <tr>
+<td class="definename">DUK_OPT_FUNC_NONSTD_CALLER_PROPERTY</td>
+<td>Add a non-standard <code>caller</code> property to non-strict function
+    instances for better compatibility with existing code.  The semantics
+    of this property are not standardized and may vary between engines;
+    Duktape tries to behave close to V8 and Spidermonkey.  See
+    <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/caller">Mozilla</a>
+    description of the property.</td>
+</tr>
+<tr>
+<td class="definename">DUK_OPT_NO_ARRAY_SPLICE_NONSTD_DELCOUNT</td>
+<td>For better compatibility with existing code, <code>Array.splice()</code>
+    has non-standard behavior by default when the second argument (deleteCount)
+    is not given: the splice operation is extended to the end of the array.
+    If this option is given, <code>Array.splice()</code> will behave in a
+    strictly conforming fashion, treating a missing deleteCount the same as
+    an undefined (or 0) value.</td>
+</tr>
+<tr>
 <td class="definename">DUK_OPT_NO_JSONX</td>
 <td>Disable support for the JSONX format.  Reduces code footprint.  Causes
     JSONX calls to throw an error.</td>