Determines the relative path of a filename from a base directory.
This method is useful in building relative links within pages of
a web site. It provides similar functionality to Anakia's
$relativePath
context variable. The arguments to
this method may contain either forward or backward slashes as
file separators. The relative path returned is formed using
forward slashes as it is expected this path is to be used as a
link in a web page (again mimicking Anakia's behavior).
This method is thread-safe.
PathTool.getRelativePath( null, null ) = ""
PathTool.getRelativePath( null, "/usr/local/java/bin" ) = ""
PathTool.getRelativePath( "/usr/local/", null ) = ""
PathTool.getRelativePath( "/usr/local/", "/usr/local/java/bin" ) = ".."
PathTool.getRelativePath( "/usr/local/", "/usr/local/java/bin/java.sh" ) = "../.."
PathTool.getRelativePath( "/usr/local/java/bin/java.sh", "/usr/local/" ) = ""