Fix test always passing in python/py-linetable.exp

The following test is found in python/py-linetable.exp:

gdb_test "python print sorted(fset)" \
    "\[20L, 21L, 22L, 24L, 25L, 28L, 29L, 30L, 32L, 33L, 37L, 39L, 40L, 42L, 44L, 45L, 46L\].*" \
    "Test frozen set contains line numbers"

I noticed that it passed when using Python 3, even though it should fail
because of the missing parentheses for the call print.

There needs to be more escaping of the square brackets. Currently, it is
interpreted as "any one character from this big list of characters,
followed by .*". When adding the required amount of backslashes, the
test starts failing as it should.

Moreover, both in Python 2.7 and Python 3.3 the numbers don't have the L
suffix, so now the test fails because of that. Anybody knows why they
were there in the first place? I just tested with Python 2.4 and there
are no Ls.

gdb/testsuite/ChangeLog:

	* gdb.python/py-linetable.exp: Escape properly sorted(fset)
	test expected output.  Add parentheses for the call to print.
	Remove L suffix from integers.

Signed-off-by: Simon Marchi <simon.marchi@ericsson.com>