Use mktemp for tempdir creation in prefetchers.

This incorporates the following two commits from <nixpkgs>:

NixOS/nixpkgs@f83af95f8a
NixOS/nixpkgs@5e7a1cf955

Hydra was the original reason why I was fixing tempdir creation in the
first place. Seeing that Hydra ships its own versions of these scripts,
we need to patch them here as well.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

src/script/nix-prefetch-bzr

@@ -43,11 +43,10 @@ fi
 # If we don't know the hash or a path with that hash doesn't exist,
 # download the file and add it to the store.
 if test -z "$finalPath"; then
-    tmpPath=/tmp/bzr-checkout-tmp-$$
-    tmpFile=$tmpPath/$dstFile
-    mkdir $tmpPath
+    tmpPath="$(mktemp -d "${TMPDIR:-/tmp}/bzr-checkout-tmp-XXXXXXXX")"
+    trap "rm -rf \"$tmpPath\"" EXIT
 
-    trap "rm -rf $tmpPath" EXIT
+    tmpFile="$tmpPath/$dstFile"
 
     # Perform the checkout.
     if test "$NIX_PREFETCH_BZR_LEAVE_DOT_BZR" != 1

src/script/nix-prefetch-git

@@ -237,11 +237,11 @@ else
   # download the file and add it to the store.
   if test -z "$finalPath"; then
 
-      tmpPath=/tmp/git-checkout-tmp-$$
-      tmpFile=$tmpPath/git-export
-      mkdir $tmpPath $tmpFile
+      tmpPath="$(mktemp -d "${TMPDIR:-/tmp}/git-checkout-tmp-XXXXXXXX")"
+      trap "rm -rf \"$tmpPath\"" EXIT
 
-      trap "rm -rf $tmpPath" EXIT
+      tmpFile="$tmpPath/git-export"
+      mkdir "$tmpFile"
 
       # Perform the checkout.
       clone_user_rev "$tmpFile" "$url" "$rev"

src/script/nix-prefetch-hg

@@ -35,11 +35,10 @@ fi
 # download the file and add it to the store.
 if test -z "$finalPath"; then
 
-    tmpPath=/tmp/hg-checkout-tmp-$$
-    tmpArchive=$tmpPath/hg-archive
-    mkdir $tmpPath
+    tmpPath="$(mktemp -d "${TMPDIR:-/tmp}/hg-checkout-tmp-XXXXXXXX")"
+    trap "rm -rf \"$tmpPath\"" EXIT
 
-    trap "rm -rf $tmpPath" EXIT
+    tmpArchive="$tmpPath/hg-archive"
 
     # Perform the checkout.
     if [[ $url != /* ]]; then