Ubuntu 15.04 compile Subsurface from source

[Steve Butler]

I suspect this morning's attempt was foiled by work's rogue external 
WiFi dropping in the middle of downloading one of the modules.   The 
attempt here at home went further/faster.  Apparently libcurl isn't part 
of 15.04.

-- checking for module 'libcurl'
--   package 'libcurl' not found
CMake Error at /usr/share/cmake-3.0/Modules/FindPkgConfig.cmake:345 
(message):
   A required package was not found
Call Stack (most recent call first):
   /usr/share/cmake-3.0/Modules/FindPkgConfig.cmake:399 
(_pkg_check_modules_internal)
   cmake/Modules/pkgconfig_helper.cmake:2 (pkg_check_modules)
   CMakeLists.txt:74 (pkg_config_library)


Will have to chase this one down tomorrow.

--Steve