Fix bug introduced in the last release that broke git-annex sync when git-annex was installed from the standalone tarball.

This was introduced by commit 450ee53ab6

However, the same problem could affect other calls to programPath,
specifically some on the assistant. So, I fixed it at a deeper level.

Annex/Path.hs

@@ -11,7 +11,9 @@ module Annex.Path where
 
 import Common
 import Config.Files
-import System.Environment
+import Utility.Env
+
+import System.Environment (getExecutablePath)
 
 {- A fully qualified path to the currently running git-annex program.
  - 
@@ -19,15 +21,22 @@ import System.Environment
  - well, it returns the complete path to the program. But, on other OSs,
  - it might return just the basename. Fall back to reading the programFile,
  - or searching for the command name in PATH.
+ -
+ - The standalone build runs git-annex via ld.so, and defeats
+ - getExecutablePath. It sets GIT_ANNEX_PROGRAMPATH to the correct path
+ - to the wrapper script to use.
  -}
 programPath :: IO FilePath
-programPath = do
+programPath = go =<< getEnv "GIT_ANNEX_PROGRAMPATH"
+  where
+	go (Just p) = return p
+	go Nothing = do
 #if MIN_VERSION_base(4,6,0)
-	exe <- getExecutablePath
-	p <- if isAbsolute exe
-		then return exe
-		else readProgramFile
+		exe <- getExecutablePath
+		p <- if isAbsolute exe
+			then return exe
+			else readProgramFile
 #else
-	p <- readProgramFile
+		p <- readProgramFile
 #endif
-	maybe cannotFindProgram return =<< searchPath p
+		maybe cannotFindProgram return =<< searchPath p