Merge pull request #428 from jankoboehm/spielwiese

Fix for Cygwin: cast to pointer from integer of different size
chg: simplified npNegM
chg: use imagemagick instead of xv for display

from master
chg: r_IsRingVar (extensions may not be singular rings, but uuse coeffs interface)
chg: factory/libfac is not optional, removing HAVE_FACTORY/HAVE_LIBFAC
fix: gcc optimizer bug: need local number variable
flint stuff: move optional parts to the end in coeffs
documenation of divisor.lib
chg: debug message: also for proc outside of libs
chg: restart nanosleep when interrupted by signal
(cherry picked from commit f9efe23dee0924e650e1aefea029b4add8fcc7e9)

Signed-off-by: Andreas Steenpass <steenpass@mathematik.uni-kl.de>
chg: announce Primdec::sep
Merge pull request #431 from steenpass/nanosleep_sw

chg: restart nanosleep when interrupted by signal
fix: wait may be undefined
chg: defer shutdown in slClose()
(cherry picked from commit 96d98ec5e074988d6acae83de7646fc65aa7382b)

Signed-off-by: Andreas Steenpass <steenpass@mathematik.uni-kl.de>

Conflicts:
	Singular/silink.cc
Merge pull request #433 from steenpass/slClose_sw

chg: defer shutdown in slClose()
chg: singularsurf/surf/display instead of gtk-surf
chg: do another waitpid() after nanosleep() succeeded
(cherry picked from commit 9d9a7faa6bb7522c1db8caabc4c47c0aa0840caf)

Signed-off-by: Andreas Steenpass <steenpass@mathematik.uni-kl.de>
fix: return NULL for non-bb-types (op2: 1st OR 2nd op is of bb type)
Merge pull request #435 from steenpass/waitpid_sw

chg: do another waitpid() after nanosleep() succeeded
fix: ring dep. stuff in newstruct: send/receive via links (ssi:6)

from master