Rename methods called from libcurl to use more clear names

Indicate that they're callbacks used by libcurl rather than normal
methods used by the application code itself.

No real changes.

include/wx/private/webrequest_curl.h

@@ -72,7 +72,8 @@ public:
 
     wxString GetError() const;
 
-    size_t ReadData(char* buffer, size_t size);
+    // Method called from libcurl callback
+    size_t CURLOnRead(char* buffer, size_t size);
 
 private:
     wxWebSessionCURL& m_sessionImpl;
@@ -104,9 +105,10 @@ public:
 
     wxString GetStatusText() const wxOVERRIDE { return m_statusText; }
 
-    size_t WriteData(void *buffer, size_t size);
 
-    size_t AddHeaderData(const char* buffer, size_t size);
+    // Methods called from libcurl callbacks
+    size_t CURLOnWrite(void *buffer, size_t size);
+    size_t CURLOnHeader(const char* buffer, size_t size);
 
 private:
     wxWebRequestHeaderMap m_headers;