Implement MString(void*) - declared but never defined

Invisible until this session's ServerCore tls/master merge brought
Subscription/SubscriptionManager (which calls it) into the same
dependency chain as a real executable for the first time - a static
library archive (ar) never checks for unresolved symbols, only the
final link of a real binary does, so this went unnoticed for however
long it sat declared-only in MString.h. Stores the raw pointer value
as the string bytes (pointer-identity comparison, matching how void*
aliases are compared everywhere else in this codebase) rather than
dereferencing it, since some callers pass arbitrary non-string
pointers through this constructor.

MString.cpp

@@ -27,6 +27,24 @@ namespace coreutils {
       memcpy(this->data, data, length);
       cursor = this->data;
    }
+
+   // Declared alongside MString(const char *data) but never implemented -
+   // invisible until a real executable actually needed this symbol
+   // resolved (a static library archive never checks for unresolved
+   // references, only the final link of a real binary does). Stores the
+   // raw pointer VALUE itself (not a dereference of it) as the string's
+   // bytes, matching how void* aliases are compared everywhere else in
+   // this codebase - by pointer identity, not by string content (e.g.
+   // TCPServer::getSessionByAlias() and TCPSession::compareAlias() both
+   // compare void* aliases directly) - so two MStrings built from the
+   // same alias value compare equal, and one built from an arbitrary
+   // (possibly non-string, possibly not even null-terminated) alias
+   // pointer never risks reading past it.
+   MString::MString(void *alias) {
+      setSize(sizeof(void *));
+      memcpy(this->data, &alias, sizeof(void *));
+      cursor = this->data;
+   }
    
    MString::MString(char *data, size_t length) {
       setSize(length);