Merge pull request #963 from nosami/mono-el-capitan

Don't assume that mono is on the path for El Capitan

src/app/FakeLib/EnvironmentHelper.fs

@@ -127,14 +127,20 @@ let isLinux = int System.Environment.OSVersion.Platform |> fun p -> (p = 4) || (
 /// Todo: Detect mono on windows
 let isMono = isLinux || isUnix || isMacOS
 
+let monoPath =
+    if isMacOS && File.Exists "/Library/Frameworks/Mono.framework/Commands/mono" then
+        "/Library/Frameworks/Mono.framework/Commands/mono"
+    else
+        "mono"
+
 /// Arguments on the Mono executable
 let mutable monoArguments = ""
 
 /// Modifies the ProcessStartInfo according to the platform semantics
 let platformInfoAction (psi : ProcessStartInfo) = 
     if isMono && psi.FileName.EndsWith ".exe" then 
         psi.Arguments <- monoArguments + " " + psi.FileName + " " + psi.Arguments
-        psi.FileName <- "mono"
+        psi.FileName <- monoPath
 
 /// The path of the current target platform
 let mutable TargetPlatformPrefix = 

src/app/FakeLib/ProcessHelper.fs

@@ -17,7 +17,7 @@ let startedProcesses = HashSet()
 let start (proc : Process) = 
     if isMono && proc.StartInfo.FileName.ToLowerInvariant().EndsWith(".exe") then
         proc.StartInfo.Arguments <- "--debug \"" + proc.StartInfo.FileName + "\" " + proc.StartInfo.Arguments
-        proc.StartInfo.FileName <- "mono"
+        proc.StartInfo.FileName <- monoPath
 
     proc.Start() |> ignore
     startedProcesses.Add(proc.Id, proc.StartTime) |> ignore