Official OpenSSL released versions up to and including 0.9.8i as well as

2008-09-24 stable snapshot have a buf_mem_st.length structure member with
'int' data type.

OpenSSL un-released 0.9.9 CVS version has a buf_mem_st.length structure member
with 'size_t' data type since 2007-Oct-09.

These 4 typecasts should silence compiler warnings in all cases.