Change default installation dirs for executables on Windows:

before:

  bindir  = $prefix\$pkgid
  datadir = $prefix

now:

  bindir  = $prefix\Haskell\bin
  datadir = $prefix\Haskell

datasubdir is still $pkgid, so data files for an exectuable will be
installed in $prefix\Haskell\$pkgid.

the idea is that all executables are installed in the same directory
by default, so setting PATH is easier.  Also, data files belonging to
Haskell programs are grouped together under $prefix\Haskell.

Distribution/Simple/LocalBuildInfo.hs

@@ -203,7 +203,7 @@ foreign import stdcall unsafe "shlobj.h SHGetFolderPathA"
 default_bindir :: FilePath
 default_bindir = "$prefix" `joinFileName`
 #if mingw32_HOST_OS || mingw32_TARGET_OS
-	"$pkgid"
+	"Haskell" `joinFileName` "bin"
 #else
 	"bin"
 #endif
@@ -235,7 +235,7 @@ default_datadir :: PackageDescription -> IO FilePath
 default_datadir pkg_descr
 #if mingw32_HOST_OS || mingw32_TARGET_OS
 	| hasLibs pkg_descr = getCommonFilesDir
-	| otherwise = return "$prefix"
+	| otherwise = return ("$prefix" `joinFileName` "Haskell")
 #else
 	= return  ("$prefix" `joinFileName` "share")
 #endif

doc/Cabal.xml

@@ -1438,7 +1438,7 @@ runhaskell Setup.hs unregister --gen-script</screen>
 
 		<row>
 		  <entry><literal>--bindir</literal></entry>
-		  <entry><literal>$prefix\$pkgid</literal></entry>
+		  <entry><literal>$prefix\Haskell\bin</literal></entry>
 		  <entry><literal>$prefix/bin</literal></entry>
 		</row>
 
@@ -1462,7 +1462,7 @@ runhaskell Setup.hs unregister --gen-script</screen>
 
 		<row>
 		  <entry><literal>--datadir</literal> (executable)</entry>
-		  <entry><literal>$prefix</literal></entry>
+		  <entry><literal>$prefix\Haskell</literal></entry>
 		  <entry><literal>$prefix/share</literal></entry>
 		</row>