With current version of Gnash, when user tried to run `./configure` script
without Csound tools installed on the system, it would show a following message:

        WARNING: You need to have csound installed
                 to have real fun.
                 Install it from http://www.csounds.com/
                 or .deb users: apt-get install csound
                 or .rpm users: yum install csound

Instead of "to have real fun", the message should show what exactly Csound
have to do with Gnash's build process or testing process; allowing user
to make an informed decision whether to install it or not.

In this case, according to `testsuite/media/Makefile.am`, Csound is used
for generating some audio files for Gnash's audio-related test cases.

Proposed patch changes the message to:

        WARNING: You need to have csound installed to generate some of
                 sound-related test files in Gnash testsuite.
                 Install it from http://www.csounds.com/
                 or .deb users: apt-get install csound
                 or .rpm users: yum install csound

Note: this patch uses `PKG_WAR()`, `PKG_SUGGEST()`, `DEB_INSTALL()`,
and `RPM_INSTALL()` macro facility instead of printing directly to fd 4.

Gnash: 0.8.11dev (patched against git f0f66ce 23-Sep-2015)
CSound: libcsound64-5.2 1:5.17.11~dfsg-3 (debian)
System: Debian GNU/Linux 7.0 Wheezy i386