windows: Add preliminary WSL support for npm and npx

This commit would make it possible to run `npm` installed on Windows within Windows Subsystem for Linux.

It is required, however, that the end of line characters of `npm` and `npx` be `\n` for the fix to take effect.

PR-URL: npm#253
Credit: @infinnie
Close: npm#253
Reviewed-by: @claudiahdz

bin/npm

@@ -8,6 +8,10 @@ case `uname` in
 esac
 
 NODE_EXE="$basedir/node.exe"
+if [ -x "$NODE_EXE" ] && [ -f "/bin/wslpath" ]; then # run the corresponding command prompt when Node for Windows is executed within WSL
+  cmd.exe /c `wslpath -w "$basedir/npm.cmd"` "$@"
+  exit $?
+fi
 if ! [ -x "$NODE_EXE" ]; then
   NODE_EXE="$basedir/node"
 fi

bin/npx

@@ -8,6 +8,10 @@ case `uname` in
 esac
 
 NODE_EXE="$basedir/node.exe"
+if [ -x "$NODE_EXE" ] && [ -f "/bin/wslpath" ]; then # run the corresponding command prompt when Node for Windows is executed within WSL
+  cmd.exe /c `wslpath -w "$basedir/npx.cmd"` "$@"
+  exit $?
+fi
 if ! [ -x "$NODE_EXE" ]; then
   NODE_EXE=node
 fi