* src/visibility.c (gpgrt_set_alloc_func): New.
* configure.ac (_ESTREAM_PRINTF_REALLOC): Define.
(_ESTREAM_PRINTF_EXTRA_INCLUDE): Define.
* src/estream.c (mem_alloc, mem_realloc, mem_free): Simplify.
(_gpgrt_free): Remove.
* src/init.c (custom_realloc): New var.
(_gpgrt_set_alloc_func): New.
(_gpgrt_realloc, _gpgrt_malloc, _gpgrt_free): New.
* src/visibility.h (gpg_err_deinit): Mark as visible.