Makefile: Also remove old versions of libiio

Otherwise they will cause a build failure when building the test
programs.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
IIOD: Correctly exit the R/W thread when the buffer creation fails

It was previously deadlocking on the "last_cond" condition variable,
which is only signaled when CLOSE is used, which never happens if OPEN
fails.

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>
Local backend: Issue an error if the buffer size requested is too big

Signed-off-by: Paul Cercueil <paul.cercueil@analog.com>