and add debugging information around its checks.

expect an index instead of a pointer

All calls referenced lastSelectionOwner so let the function directly
use it and only pass the required index.

Attributes GH PR #884: https://github.com/ArcticaProject/nx-libs/pull/884

no more hardcoded string length

no more hardcoded string length

no more hardcoded string length

Error.c: In function ‘nxagentGetSessionPath’:
Error.c:543:62: warning: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 253 [-Wformat-truncation=]
     snprintf(nxagentSessionDir, DEFAULT_STRING_LENGTH, "%s/C-%s", rootPath, nxagentSessionId);
                                                              ^~             ~~~~~~~~~~~~~~~~
Error.c:543:5: note: ‘snprintf’ output 4 or more bytes (assuming 259) into a destination of size 256
     snprintf(nxagentSessionDir, DEFAULT_STRING_LENGTH, "%s/C-%s", rootPath, nxagentSessionId);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dialog.c: In function ‘nxagentLaunchDialog’:
Dialog.c:320:53: warning: ‘%s’ directive output may be truncated writing up to 1023 bytes into a region of size 256 [-Wformat-truncation=]
     snprintf(dialogDisplay, sizeof(dialogDisplay), "%s", nxagentDisplayName);
                                                     ^~   ~~~~~~~~~~~~~~~~~~
Dialog.c:320:5: note: ‘snprintf’ output between 1 and 1024 bytes into a destination of size 256
     snprintf(dialogDisplay, sizeof(dialogDisplay), "%s", nxagentDisplayName);
     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Attributes GH PR #607: https://github.com/ArcticaProject/nx-libs/pull/607

Make nxproxy and nxagent print an arbitrary version number by running
make NX_VERSION_CUSTOM="myvers". nxagent and nxproxy will then show
this in addition to the original version number:

NXPROXY - Version myvers (3.5.99.22)
NXAGENT - Version myvers (3.5.99.22)

Fixes ArcticaProject/nx-libs#606

Attributes GH PR #883: https://github.com/ArcticaProject/nx-libs/pull/883

XlibAtom should be used wherever remote atoms are handled. This is
important as Xlib data types and server data types of the same name do
not always have identical sizes.

See also https://lists.freedesktop.org/archives/xorg-devel/2015-August/047245.html

Attributes GH PR #869: https://github.com/ArcticaProject/nx-libs/pull/869