curl_global_init_mem.3: Stronger thread safety warning

allows the application to set callbacks to replace the otherwise used internal

memory functions.

When you use this function, all callback arguments must be set to valid

function pointers. \fBIf you are using libcurl from multiple threads or with

the threaded resolver (the default in Windows) the callback replacement

functions must be thread safe.\fP

If you are using libcurl from multiple threads or libcurl was built with the

threaded resolver option then the callback functions must be thread safe. The

threaded resolver is a common build option to enable (and in some cases the

default) so we strongly urge you to make your callback functions thread safe.

The prototypes for the given callbacks should match these:

All callback arguments must be set to valid function pointers. The

prototypes for the given callbacks must match these:

.IP "void *malloc_callback(size_t size);"

To replace malloc()

.IP "void free_callback(void *ptr);"