[Rxtx] `which java` should be `dirname \`which java\` ` in configure script

[hama at cyberonix.co.jp]

Hi,

I found some mistake in configure file derived from configure.in .
`which java` is used 4 times.
They should be 
`dirname \`which java\` `
because directory name is required for the places.

I found them when I ran ./configure on Linux, running on SH4 board.
When I run ./configure on i386 machine, the path isn't used.
------------------------------------------------
  Takeshi "Ken" Hamasaki :  hama at cyberonix.co.jp