add LOCK() for proxy related data-structures

- fix #1560 by properly locking proxy related data-structures
- update GetProxy() and introduce GetNameProxy() to be able to use a
  thread-safe local copy from proxyInfo and nameproxyInfo
- update usage of GetProxy() all over the source to match the new
  behaviour, as it now fills a full proxyType object
- rename GetNameProxy() into HaveNameProxy() to be more clear

src/net.cpp

@@ -1185,7 +1185,7 @@ void ThreadDNSAddressSeed2(void* parg)
         printf("Loading addresses from DNS seeds (could take a while)\n");
 
         for (unsigned int seed_idx = 0; seed_idx < ARRAYLEN(strDNSSeed); seed_idx++) {
-            if (GetNameProxy()) {
+            if (HaveNameProxy()) {
                 AddOneShot(strDNSSeed[seed_idx][1]);
             } else {
                 vector<CNetAddr> vaddr;
@@ -1529,7 +1529,7 @@ void ThreadOpenAddedConnections2(void* parg)
     if (mapArgs.count("-addnode") == 0)
         return;
 
-    if (GetNameProxy()) {
+    if (HaveNameProxy()) {
         while(!fShutdown) {
             BOOST_FOREACH(string& strAddNode, mapMultiArgs["-addnode"]) {
                 CAddress addr;