convert: add commandline.xargs(), use it in svn_sink class Introduce commandline.xargs() to limit argument list with respect to ARG_MAX bytes. If no ARG_MAX information available - use POSIX required minimum of 4096 bytes. Under Windows, while actual argument list length is limited to 32k, shells impose their own limits on command line length, down to 2047 bytes for cmd.exe under Windows NT/2k and about 2500 bytes for older 4nt.exe. See http://support.microsoft.com/kb/830473 for details about cmd.exe limitations. Since ARG_MAX is limit for argument list and environment, we reserve half of it and one byte for environment variables. This way with default ARG_MAX (4096 bytes) we get value 2047 bytes which is OK for Windows too.