[asterisk-dev] Makefile Fix.

[Fernando Lujan]

Hi guys, I just correct this two lines in the Makefile.

There are missing the -D option and giving a error when we set a DESTDIR 
variable.

386         install -D -m 644 doc/ztcfg.8 
$(INSTALL_PREFIX)/usr/share/man/man8
387         install -D -m 644 doc/zttool.8 
$(INSTALL_PREFIX)/usr/share/man/man8

Thanks.

Fernando Lujan