[s4] make install with waf does not create prefix/etc directory

[Nadezhda Ivanova]

Hello Tridge,
I am using the waf build now, and if one installs on a clean system (no
samba has been installed before), provisioning fails when smb.conf is
created, because the etc directory is missing. The problem does not appear
if one provides a targetdir to provisioning. I will fix provision.py to
check and create the etc, but since the previous build system created etc
during install, I figured you might want to know. I cant figure out by
myself how to fix it in make install, or if I should.

Regards,
Nadya