Greatly improve /proc/PID/stack by tracing the ebp frame chain.

I also added a generator cache to FileHandle. This way, multiple
reads to a generated file (i.e in a synthfs) can transparently
handle multiple calls to read() without the contents changing
between calls.

The cache is discarded at EOF (or when the FileHandle is destroyed.)

Kernel/init.cpp

@@ -65,6 +65,17 @@ Vector<KSym>& ksyms()
     return *s_ksyms;
 }
 
+const KSym* ksymbolicate(dword address)
+{
+    if (address < ksyms().first().address || address > ksyms().last().address)
+        return nullptr;
+    for (unsigned i = 0; i < ksyms().size(); ++i) {
+        if (address < ksyms()[i + 1].address)
+            return &ksyms()[i];
+    }
+    return nullptr;
+}
+
 static void loadKernelMap(const ByteBuffer& buffer)
 {
     s_ksyms = new Vector<KSym>;