#1289 Parser: foreach and for loop needs to pop current_block_stack

[Henry Wong]

Segfault if a for loop (with variable declaration) or a foreach loop is used inside a named block or a block that declares variables.

Root cause seems to be parser forgetting to pop the current_block_stack after processing one of these two statements, which ends up creating a loop in the Statement tree. The segfault happens later during PBlock::elaborate_scope when it hits infinite recursion.

[Henry Wong]

Some test cases: The first three will trigger the bug, but the last doesn't.
1: Inside a block that declares a variable (reg a)
2: Inside a named block
3: The same thing with foreach
4: This passes because the initial block isn't named, and no variables are declared.

I tested with iverilog -g2012 to enable SystemVerilog features.

[Stephen Williams]

Applied to git mater.