bug in killing ring dependent attributes in Singular interpretator

[Oleksandr]

Segment fault/Bus error occurred at atKILLATTR1 :: atKillAll :: root->attribute->killAll() since the attribute is ring dependent but ring was already killed (r = 0x0)...

Test:

ring R; ideal I = maxideal(1); attrib(I, "A", ideal(var(1)));
I; attrib(I, "A");
kill R; // BUGGG
$

gives:

testa.sing   1> ring R; ideal I = maxideal(1); attrib(I, "A", ideal(var(1)));
testa.sing   2> I;
I[1]=x
I[2]=y
I[3]=z
testa.sing   3> attrib(I, "A");
_[1]=x
testa.sing   4> 
testa.sing   5. kill R;
Singular : signal 11 (v: 3101/2009050412):
current line:>>kill R;<<
Segment fault/Bus error occurred at 2b9a17bd4bc0 because of 10206 (r:1241461411)
please inform the authors

// ***dError: Caught Signal 11 occured at: 

[Oleksandr]

test

[Oleksandr]

result

[hannes]

handling of ring dep. attributes fixed