Q:

When were the analogs of the C operators "break" and "continue" introduced in Pascal?

When published in 1970, the Pascal language did not have a way to implement the functionality equivalent to the (future) C language operators "break" and "continue". Their convenience having been recognized, extended dialects of Pascal have started to feature similar operators.
From the same documentation for an implementation of Pascal for a Soviet computer as here, dated 1979:

In accordance with the ideas of structural programming and the requirements 
  of programming practice, the following control structures are introduced in the language:
Structural labels
An operator can be labeled with a structural label.
<operator> ::= { <label>: }* { ( <structural label> ) }* <unlabeled operator> 
<structural label> ::= <identifier>
The scope of a structural label is the unlabeled operator.
exit operator
Within the scope of a structural label, e. g. "(M)", there may be operators exit M, equivalent to exiting the corresponding unlabeled operator.
Syntax
<exit operator> ::= exit <structural label>
goto operator
Syntax
<goto operator> ::= goto ( <label> | <structural label> )
A goto operator using a structural label may appear within the scope 
  of that structural label. Its function is equivalent to the regular 
  goto operator.
Structural labels realize the right of each operator to iterate and to complete.

(Most readers of the documentation would later misquote the last statement as "the inalienable right of each operator to iterate and to complete".)
TL;DR: Structural labels implement mechanisms akin to generalized "break" and "continue" operators on the C language. For example:
(outerloop) for i := 1 to 100 do
(innerloop) for j := 1 to 100 do
     (iter) begin
            ...
            exit iter; { same as continue in C }
            ...
            exit innerloop; { same as break in C }
            ...
            exit outerloop; { no convenient C analog }
     end

Unlike regular numerical labels in Pascal, structural labels did not need to be pre-declared.
Turbo Pascal appeared in the 1980s and seems to have regular C-like break and continue.

The question is: Has any pre-1979 dialect of Pascal featured "structural labels", or any kind of break/continue functionality?

A:

It is difficult to say for sure, because there have been a lot of implementations of the Pascal Language (some of them not very widely distributed), each with their own specific additions to the language.
Anyway, my researchs show that it is very unlikely that a feature like the one you describe have been made available before 1979:

The Turbo Pascal compiler (which has certainly been one of the most widely ditributed Pascal implementations, and stands, at least for me, as a reference) has, indeed, introduced break/continue statements, but not before the 7.0 version, released in 1992. See the reference manuals available here. In a paragraph named "Flow control procedures", you'll see the break/continue statements are mentioned for the 7.0 version, but not for the 6.0 version.
The Pascal MT+, released in 1980, show no such thing in its reference manual (available here).
The UCSD Pascal, released in 1978, is simply based on the Wirth definition of Pascal with a few additions, but nothing that looks like a break/continue statement (manual here).

I made some additional researchs on other implementations, but almost all of them are said to be close to the ISO 7185 standard, and I couldn't find the manuals online.
Anyway, the fact that Borland introduced this feature so late (and that nobody answered this question yet) should be convincing enough. I may have missed some very obscure implementations, though (like the one you mention).

