1054 – regression: circular aliases cause compiler stack overflow

# alias a b;
# alias b a;
#
# b x;
dmd -c a.d -> segfaults
# alias a b;
# alias b a;
dmd -c a.d -> compiles even though it shouldn't
test cases:
http://dstress.kuehne.cn/nocompile/a/alias_30_G.d
http://dstress.kuehne.cn/nocompile/a/alias_30_J.d
http://dstress.kuehne.cn/nocompile/a/alias_30_K.d
http://dstress.kuehne.cn/nocompile/e/enum_44_E.d 

*** Bug 1063 has been marked as a duplicate of this bug. ***

The first case no longer segfaults -- it stack overflows instead, and the second case now generates an error.
On DMD1.042, the first case displays:
fog.d(2): Error: alias fog.a recursive alias declaration
Stack overflow
and on DMD2.027, it gets caught in an infinite loop:
fog.d(2): Error: alias fog.a recursive alias declaration
fog.d(2): Error: alias fog.a recursive alias declaration
fog.d(2): Error: alias fog.a recursive alias declaration
fog.d(2): Error: alias fog.a recursive alias declaration
fog.d(2): Error: alias fog.a recursive alias declaration

This is fixed in DMD2.030, but not in DMD1.045.
alias a b;
alias b a;
a y;
---
ice.d(544): Error: alias ice.a recursive alias declaration
Stack overflow
----------

Fixed dmd 1.046