dynamically insert prefix path into init script

using sed -i when running make install
xrdp initscript add BASE var, add SDAEMON var, replace fullpaths

with combined path var

-DAEMON=/usr/sbin/xrdp

+BASE=__BASE__
(PREFIX gets replaced by given prefix, or as fallback /usr/local on Ubuntu)

+DAEMON=${BASE}/sbin/xrdp
+SDAEMON=${BASE}/sbin/xrdp-sesman
Merge pull request #86 from cocoon/master

Dynamically build initscript paths from given prefix