Package mapsoft2: Information

- image_cnt, srtm, ms2geofig: add tracing of rivers and mountain
  ridges (my old code from mapsoft1 with some improvements);
  move code for finding summits to image_cnt; fix SRTM::get_img() method
  and use it for contour and summit tracing to avoid data smoothing;
  cleanup code and tests in image_cnt.
- geom/poly_tools.h: add join_cross function (join crossing parts of a MultiLine);
  use it in vmap2 when saving fig and gpx; use it in ms2geofig when tracing steep slopes.
- image: add ImageR::get_double_range method
- srtm: fix error in deg->m conversion
- downloader: fix test for libcurl>=8.9.0 (fix altlinux.build)
- cairo: remove deprecated functions
- fix a few memory-handling problems (thanks to valgrind)

image:
 - Add support for reading tiled TIFF images
 - An important fix for tiled image data handling (much faster rendering)
 - Fix slazav/mapsoft2#67 error (important for new libtiff)
 - A few fixes and interface changes
image_cnt - new module:
 - Finding contours on the image, smart contour filtering
srtm:
 - Rewrite data handling and interpolation (one more time)
 - Fix data handling for much faster operation
 - Using image_cnt module
 - Using overlay data (see https://github.com/slazav/alos_overlay)
vector maps:
 - remove set_dpi command in types.cfg; set fig font size for each object separately
 - improve default label positions: move to the nearest object point; label_def_mshift option
vmap_data:
 - types.cfg: adjust fig font size, add label_def_mshift for some objects
 - render.cfg: tune fonts for summits and passes
 - always use UTF8 encoding in fig files
 - vmaps_wp_update: use single wpasses.cnv
ms2geofig program:
 - apply --cnt_minpts option only to closed contours
 - new contour finding; add cnt_vtol, scnt_vtol options; remove smooth option
 - --add_comm option (adding additional comments to new fig objects)

A few bug fixes:
- err: fix problems with NaN values and with multiple evaluations in assert scripts
- geom/line_walker: avoid NaN values for lines with repeated points
- fig: fix scaling/shifting
- srtm: fix error in find_peaks(), fix error with getting points between tiles
- vmap2gobj: fix problem with short_expand feature applied to zero-length lines
- vmap2: optional scale argument to fig_pic command in types file
- viewer/gobj_multi: set trivial cnv in constructor, check for NULL cnv