replace hostent lookup with better performing in-memory copy.

the central dns resolver function proxy_gethostbyname() used
to iterate over the gethostent() db (/etc/hosts) on each dns
request.
since this is not threadsafe, we synchronized access to it
previously using mutexes. the parsing of this file is slow,
and blocking all threads to do it even moreso.
since gethostent_r() is only available on a few platforms,
i decided to read the hostent db once and then use a quick
in-memory lookup on further usage.

+ some further refactoring.

src/stringdump.h

@@ -0,0 +1,12 @@
+#ifndef STRINGDUMP_H
+#define STRINGDUMP_H
+
+#include "shm.h"
+#include <unistd.h>
+
+char *dumpstring(char* s, size_t len);
+void dumpstring_init(void);
+
+//RcB: DEP "stringdump.h"
+
+#endif