add unused mutex.H related to researching ||ism approaches
mutex.H: further explorations of ||ism options
img_io: split impl of set_size_and_alloc_pels() into set_size() and alloc_pels() to allow custom external alloc via set_size() followed by setting .pels.
nesi: add int32_t support
error handling bugfix for EINTR; add 'r' debugging/testing key command to set img[0] to grey.
boda_base: add first pass at make_mmap_shared_p_uint8_t()
cap_util: use general boda mmap buffer function instead of local custom version