Keep ECPG comment for log_min_duration_statement

Hi,

I'd like to make it easier to analyze slow queries in ECPG using
log_min_duration_statement. Especially when DBA and C application developer
is different, DBA can feedback slow embedded query to the developer without
difficulty and mistakes.

When our customers log and look into slower queries in C programs with
embedded SQL, they use log_min_duration_statement.Using this logging option,
SQL statement slower than a threshold will be displayed, but comments won't.
That's because the pre-compiler (ECPG) removes all the comments when the
pre-compiler converts C with embedded SQL to normal C code.

Without comments, DBA has difficulty with identifying to which C code
the slow query belongs. And the exact slow query issue cannot be reported
to the developer.
So, I'd like to modify ecpg command not to remove some specific comments.

[Use-cases]
Here is a scenario:
1) Writing comments to embedded C file
a) Describe the detailed usage of SQL in each comment.

b) Allocating id to each SQL.
- application developer need to create corresponding table between id
and the detailed description of SQL

2) DBA takes advantage of comments especially when:
a) Similar comments are displayed here and there.
In such a case, each comment plays a role as an identifier and makes it
easier for DBA to identify SQL he/she looking for.
b) DBA and C application developer are different.
DBA can tell an application developer which query is slow without mistakes.

[Interface]
add a new option "--enable-parse-comment" to ecpg command.

<usage> ecpg --enable-parse-comment ,..., prog.pgc

This option enables ecpg command to pass on block comments (/* 〜 */) to converted C file.
The conditions to enable processing "block comments" as follows:
- a block comment can be used with SELECT, INSERT, UPDATE, or DELETE
- a block comment can be placed right after keywords: SELECT, INSERT, UPDATE, DELETE or With
- other than those above error will occur
- line comment(--) are ignored, which is same as log output when logging libpq application

[Example]
1)[Correct comment position] this comment position is right after SELECT
EXEC SQL SELECT /* qid=3, at line 30 in yourApp.ecpg */ * INTO :C1, :C2 FROM T1 WHERE C1=1;

2)[Incorrect comment position] this comment position is bad（error will occur)
EXEC SQL /* qid=3, at line 30 in yourApp.ecpg */ SELECT * INTO :C1, :C2 FROM T1 WHERE C1=1;

As far as I searched, there seems no discussion on this topic.
Please let me know if exists.

Regards,
Okano Naoki
Fujitsu