version-check: added brief documentation

#!/usr/bin/env perl

#***************************************************************************

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#  Project                     ___| | | |  _ \| |

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#                            | (__| |_| |  _ <| |___

#                             \___|\___/|_| \_\_____|

#

# Copyright (C) 1998 - 2010, Daniel Stenberg, <daniel@haxx.se>, et al.

#

# This software is licensed as described in the file COPYING, which

# you should have received as part of this distribution. The terms

# are also available at http://curl.haxx.se/docs/copyright.html.

#

# You may opt to use, copy, modify, merge, publish, distribute and/or sell

# copies of the Software, and permit persons to whom the Software is

# furnished to do so, under the terms of the COPYING file.

#

# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY

# KIND, either express or implied.

#

###########################################################################

# This script accepts a source file as input on the command line.

#

# It first loads the 'symbols-in-versions' document and stores a lookup

# table for all known symbols for which version they were introduced.

#

# It then scans the given source file to dig up all symbols starting with CURL.

# Finally, it sorts the internal list of found symbols (using the version

# number as sort key) and then it outputs the most recent version number and

# the symbols from that version that are used.

#

# Usage:

#

#    version-check.pl [source file]

#

open(S, "<../libcurl/symbols-in-versions") || die;