Create BIO_read_ex() which handles size_t arguments

Also extend BIO_METHOD to be able to supply an implementation for the new
BIO_read function.

Reviewed-by: Richard Levitte <levitte@openssl.org>

include/internal/bio.h

diff --git a/include/internal/bio.h b/include/internal/bio.h
index 3b6a6ac..f840bcd 100644
--- a/include/internal/bio.h
+++ b/include/internal/bio.h
@@ -13,7 +13,8 @@
     int type;
     const char *name;
     int (*bwrite) (BIO *, const char *, int);
-    int (*bread) (BIO *, char *, int);
+    int (*bread) (BIO *, char *, size_t, size_t *);
+    int (*bread_old) (BIO *, char *, int);
     int (*bputs) (BIO *, const char *);
     int (*bgets) (BIO *, char *, int);
     long (*ctrl) (BIO *, int, long, void *);
@@ -24,3 +25,7 @@
 
 void bio_free_ex_data(BIO *bio);
 void bio_cleanup(void);
+
+
+/* Old style to new style BIO_METHOD conversion functions */
+int bread_conv(BIO *bio, char *out, size_t outl, size_t *read);