Zero out entire net_wm structures using memset

Compiling with -Wall gives:

misc.c: In function ‘get_net_wm_state’:
misc.c:404:22: warning: argument to ‘sizeof’ in ‘bzero’ call is the same expression as the destination; did you mean to dereference it? [-Wsizeof-pointer-memaccess]
     bzero(nws, sizeof(nws));

This is fixed by using sizeof(*nws). Same fix in get_net_wm_window_type.

Additionally, prefer memset over bzero.
Ignore *.o, *.dep, executable
Merge pull request #19 from osandov/master

A couple of fixes