libtorrent: cleaned .conf to reduce duplication

network/libtorrent/libtorrent.conf

@@ -12,12 +12,9 @@
 # GNU General Public License can be found in the file COPYING.
 # --- SDE-COPYRIGHT-NOTE-END ---
 
-# libtorerent is unable to find boost threads on its own :-/
-var_append confopt ' ' '--with-boost-system=boost_system-mt'
-var_append confopt ' ' '--with-boost-asio=boost_system-mt'
-var_append confopt ' ' '--with-boost-filesystem=boost_filesystem-mt'
-var_append confopt ' ' '--with-boost-thread=boost_thread-mt'
-var_append confopt ' ' '--with-boost-regex=boost_regex-mt'
-var_append confopt ' ' '--with-boost-python=boost_python-mt'
-var_append confopt ' ' '--with-boost-program_options=boost_program_options-mt'
+# libtorrent is unable to find boost threads on its own :-/
+for x in asio:system system filesystem thread regex python \
+	program_options; do
 
+	var_append confopt ' ' "--with-boost-${x%:*}=boost_${x#*:}-mt"
+done