Instead of throwing luaL_error() for bad arguments, use luaL_argcheck() and
luaL_argerror() for more descriptive messages.
Store the 'textadept' table's 'buffers', 'views', 'constants',
'buffer_functions', and 'buffer_properties' tables in the Lua registry and refer
to them via metatables so that overwrites are not possible; removed 'rawset'
for Lua scripts.
Double-clicking a search result will open the file in the previous view (if it
exists) rather than clobbering the current one. Also added the find text to the
output.
