Remove hardcoding of path from desktop file and launcher script. Patch by vincent. Fixes #1424.

This was SVN commit r13365.

build/resources/0ad.desktop

@@ -3,7 +3,7 @@ Version=1.0
 Name=0 A.D.
 Comment=A real-time strategy game of ancient warfare
 Comment[it]=Videogioco strategico in tempo reale di guerre antiche
-Exec=/usr/bin/0ad
+Exec=0ad
 Icon=0ad
 Terminal=false
 Type=Application

build/resources/0ad.sh

@@ -1,3 +1,9 @@
 #!/bin/sh
 
-/usr/bin/pyrogenesis "$@"
+pyrogenesis=$(which pyrogenesis 2> /dev/null)
+if [ -x "$pyrogenesis" ] ; then
+  "$pyrogenesis" "$@"
+else
+  echo "Error: pyrogenesis not found in ($PATH)"
+  exit 1
+fi