[BUG FIX]Connection fails with whitespace after keepalives parameter value

Hi hackers,

I've discovered a bug in ECPG that causes database connection failures. This issue
appears to stem from libpq layer.

Found bug: The EXEC SQL CONNECT TO statement fails to connect to the database.
Specifically, the following code:

```c
EXEC SQL CONNECT TO tcp:postgresql://localhost:5432/postgres?keepalives=1
&keepalives_idle=1 USER yuto;
```

When precompiled and executed, this code fails to connect to the database.
Error message:

```
failed: keepalives parameter must be an integer
```

Steps to reproduce: The issue can be reproduced using the attached pgc file.

Root cause: The method for parsing the keepalives parameter in the useKeepalives
function of the libpq library is not appropriate. Specifically, it doesn't
account for whitespace following the numeric value.

Proposed fix: strtol() can be replaced with pqParseIntParam() like other paramters.
This skips whitespaces.

Concerns:
1. This fix may limit parameter values to integers only.
Example: keepalives=2147483648 (values larger than INT_MAX can't be read)
2. Whitespace after '=' that was previously not read will now be read.
Example: keepalives= 1 (previously couldn't be read, now read as 1)
3. This issue was introduced in previous versions (as far as I could verify,
from 9.0), so we may need to consider backpatching if necessary.

These concerns warrant further discussion.

I'd appreciate your review of this patch and these concerns. Thank you.