Relax cabal version requirement to 1.18+

The cabal version 1.20+ was required only for the --required-sandbox
flag. However since the make files are setting up the sandbox we know
that we are always building using sandbox. The current Haskell Platform
comes with cabal 1.18 so this way installing cabal update is not needed.

README.md

@@ -24,7 +24,7 @@ The Bond repository uses Git submodules and should be cloned with the
     git clone --recursive https://github.com/Microsoft/bond.git
 
 In order to build Bond you will need CMake (2.8.12+), Haskell (ghc 7.4+ and 
-cabal-install 1.20+) and Boost (1.54+). The core Bond C++ library can be used 
+cabal-install 1.18+) and Boost (1.54+). The core Bond C++ library can be used 
 with C++03 compilers, although Python support, unit tests and various examples 
 require some C++11 features.
 
@@ -131,12 +131,7 @@ Install the following tools:
 - CMake ([http://www.cmake.org/download/](http://www.cmake.org/download/))
 - Haskell Platform ([http://haskell.org/platform/](http://haskell.org/platform/))
 
-
-Update cabal to the latest version (if behind a proxy, set environment variable 
-`HTTP_PROXY=http://proxy:port` before running cabal):
-
-    cabal update
-    cabal install cabal-install
+If behind a proxy, set environment variable `HTTP_PROXY=http://proxy:port`.
 
 Now you are ready to build the C# version of Bond. Open the solution file 
 `cs\cs.sln` in Visual Studio 2013 and build as usual. The C# unit tests can 

appveyor.yml

@@ -32,7 +32,6 @@ install:
         cabal update
 
     }
-- cmd: cabal install cabal-install
 # Majority of build time is spent installing dependencies and then building
 # cabal and the sandbox. Using build matrix support we would have to do this
 # for every configuration. Instead we manually build the configurations we want

compiler/CMakeLists.txt

@@ -4,7 +4,7 @@ set (CMAKE_MODULE_PATH
     ${CMAKE_CURRENT_SOURCE_DIR}/../cmake)
 
 # required Haskell components
-find_package (Cabal 1.20.0.0 REQUIRED)
+find_package (Cabal 1.18.0.0 REQUIRED)
 find_package (GHC 7.4.1.0 REQUIRED)
 
 set (sources

compiler/cabal.config

@@ -1 +0,0 @@
-require-sandbox: True

compiler/cabal_build.cmake

@@ -7,7 +7,7 @@
 # As a workaround we execute this .cmake script as a custom command and use CMake
 # cache to get access to variables set during configuration.
 execute_process (
-    COMMAND ${Haskell_CABAL_EXECUTABLE} --require-sandbox install   --with-compiler=${Haskell_GHC_EXECUTABLE} --only-dependencies --jobs
+    COMMAND ${Haskell_CABAL_EXECUTABLE} install   --with-compiler=${Haskell_GHC_EXECUTABLE} --only-dependencies --jobs
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
     RESULT_VARIABLE error)
 
@@ -16,7 +16,7 @@ if (error)
 endif()
 
 execute_process (
-    COMMAND ${Haskell_CABAL_EXECUTABLE} --require-sandbox configure --with-compiler=${Haskell_GHC_EXECUTABLE} --builddir=${output_dir}
+    COMMAND ${Haskell_CABAL_EXECUTABLE} configure --with-compiler=${Haskell_GHC_EXECUTABLE} --builddir=${output_dir}
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
     RESULT_VARIABLE error)
 
@@ -25,7 +25,7 @@ if (error)
 endif()
     
 execute_process (
-    COMMAND ${Haskell_CABAL_EXECUTABLE} --require-sandbox build     --with-ghc=${Haskell_GHC_EXECUTABLE} --ghc-option=-O2 --jobs --builddir=${output_dir}
+    COMMAND ${Haskell_CABAL_EXECUTABLE} build     --with-ghc=${Haskell_GHC_EXECUTABLE} --ghc-option=-O2 --jobs --builddir=${output_dir}
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
     RESULT_VARIABLE error)