VBOX: Add code to handle search path modification for Linux and Mac.

Something has changed on OS X that prevents /usr/local/bin from being in the default search path.  It is when launched from a terminal window, but not when BOINC launches vboxwrapper.  I think recent versions of VirtualBox changed where it stores VboxManage on install.  bbad0d9 recently addressed this in the CC.

samples/vboxwrapper/vbox_vboxmanage.cpp

@@ -86,8 +86,6 @@ int VBOX_VM::initialize() {
 
     // Prep the environment so we can execute the vboxmanage application
     //
-    // TODO: Fix for non-Windows environments if we ever find another platform
-    // where vboxmanage is not already in the search path
 #ifdef _WIN32
     if (!virtualbox_install_directory.empty())
     {
@@ -98,6 +96,18 @@ int VBOX_VM::initialize() {
             vboxlog_msg("Failed to modify the search path.");
         }
     }
+#else
+    old_path = getenv("PATH");
+    if(boinc_file_exists("/usr/local/bin/VboxManage")) {
+        new_path = "/usr/local/bin/:" + old_path;
+    }
+    if(boinc_file_exists("/usr/bin/VboxManage")) {
+        new_path = "/usr/bin/:" + old_path;
+    }
+    // putenv does not copy its input buffer, so we must use setenv
+    if (setenv("PATH", const_cast<char*>(new_path.c_str()), 1)) {
+        vboxlog_msg("Failed to modify the search path.");
+    }
 #endif
 
     // Determine the VirtualBox home directory.  Overwrite as needed.