Merge pull request #370 from YueRen/spielwiese

chg: removed 'extern "C"' around declaration of feOptHelp and feGetOptValue
chg: improve definiteGcdCancellation by using singclap_gcd_and_divide
chg: handle nested fractions in singclap_gcd_and_divide
chg: updated test results
Merge pull request #371 from mmklee/cancellation

Cancellation
experimental: several links to the same port
(cherry picked from commit 0e368b1eaeedc0d3bf686832d825f5da7bc3a81b)

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

Conflicts:
	Singular/extra.cc
	Singular/links/ssiLink.cc (changes already ported)
chg: deleted unnecessary p_Content
chg: make monic if not over Q
Fix "if (deg=0)" in new exp. coeffs (see issue #374)
Merge pull request #372 from steenpass/changes_from_master

experimental: several links to the same port
fix: cddgmp test (with static libs)
chg: allow assignment def=def (for "undefinig" list entries)
(cherry picked from commit a5281ab5104ed2cc0fc7a91c462921c5ebe96bbe)

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

Conflicts:
	Singular/ipassign.cc
fix: allow assignment def=def (for "undefinig" list entries)
(cherry picked from commit ee5be4b44ef3710c997a64552e4bf48a604dd4b3)

Signed-off-by: Andreas Steenpass <steenpass@mathematik.uni-kl.de>
fix: allow assignment def=def (for "undefinig" list entries)
(cherry picked from commit 1b84dbde061938b92415371f1390ed6c3f31d328)

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

Conflicts:
	Singular/table.h
Merge pull request #376 from steenpass/changes_from_master

Changes from master: allow assign of unused list elements
(needed in corner cases in libs)
fix: mac osx port: need extern int in a c file (D, not C code part)
chg: add optional warning for ring variables names used in procedures
chg: updated test results for primitiv_l.tst
Merge pull request #381 from mmklee/primitiv_test

chg: updated test results for primitiv_l.tst
added missing bug_tr485 test (see 4c0f1bb48b8)
chg: replaced all n_* with np* functions to reduce overhead